REGULATION OF PLANT GROWTH

Abstract: The invention relates to the molecular cloning and expression of a gibberellin (GA) 20-oxidase gene and its use, for example in transgenic plants. Aspects of the invention include recombinant DNA which encodes a polypeptide exhibiting GA 20-oxidase activity, a recombinant polypeptide exhibiting GA 20-oxidase activity, and transgenic plants which express a GA 20-oxidase gene or reverse GA 20-oxidase sequences.

Description: REGULAΗON OF PLANT GROWTH This invention relates to the regulation of plant growth, and more particularly to the molecular cloning and expression of a gibberellin 20-oxidase gene and its use, for example in transgenic plants. Chemical compounds for control of plant growth have been in commercial use for many years. Many of these compounds act by inhibiting various steps in the biosynthesis of gibberellins (GAs). GAs form a large group of diterpenoid natural products, some members of which function as hormones in plants, controlling many aspects of develop¬ ment, including for example shoot elongation. Among the groups of compounds which inhibit GA biosynthesis in higher plants are quaternary ammonium and phosphonium compounds, compounds with a nitrogen-containing heterocycle, and acylcyclohexane- diones. However, the use of such chemicals involves several problems. It is, for example, difficult to apply the chemicals to plants in the appropriate quantities, or to select plant organs, without the chemicals spreading to other plants or animal life. There is a risk of persistence which can make it difficult to grow other crops subsequently to treated crops. A problem addressed by the present invention is therefore to avoid the use of such chemicals. This problem can be solved within this application by providing means for plant growth control at the plant gene level. The later steps of the GA biosynthetic pathway include those shown in Figure 1 of the accompanying drawings, which provides the structure of GAs discussed in this applica¬ tion and their metabolic relationships. These steps are catalysed by soluble 2-oxo- glutarate-dependent dioxygenases, several of which have been proposed as regulatory enzymes in the biosynthesis of the physiologically important C19 compound, GAj. For example, the activity of the GA 20-oxidase is enhanced by long days in certain photo- period-sensitive plants and is down-regulated as a consequence of GAj action in several species. According to the invention, there is provided a DNA sequence which encodes a poly¬ peptide exhibiting GA 20-oxidase activity. This disclosure is the first example of the molecular cloning of a GA:2-oxoglutarate dioxygenase. The enzyme GA 20-oxidase is also known as a 20-hydroxylase or C-20 oxidase, as it catalyses oxidation reactions at the C-20 carbon atom of the GA structure. It is a dioxygenase, as oxoglutarate is simultane¬ ously oxidised. As demonstrated in the Examples the DNA sequence of the present invention encodes GA 20-oxidase capable of acting essentially on one or more of the following substrates: GA12. GA53, GA15 (open or closed lactone), GA44 (open or closed lactone), GA24, GA19 and GA23 among others. The present invention thus further relates to a DNA sequence encoding a polypeptide exhibiting GA 20-oxidase activity, in which the polypeptide exhibiting GA 20-oxidase activity is capable of acting essentially on one or more of the following substrates: GAj2» GA53, GA15 (open or closed lactone), GA44 (open or closed lactone), GA24, GA19 and GA 2 3 The DNA sequence of the invention may encode a GA 20-oxidase from, in principle, any plants or fungi, but preferably from monocotyledonous and dicotyledonous plants, and more preferably from dicotyledonous plants. A particularly suitable source is plants of the family Cucurbitaceae, such as C. maxima, of which the immature seeds are a convenient source. A further suitable source is plants of the family Cruciferae, such as Arabidopsis thaliana, of which shoot material is a convenient source. A preferred embodiment of the invention is therefore a DNA sequence which encodes a GA 20-oxidase obtainable from plants or fungi, preferably from monocotyledonous and dicotyledonous plants respectively, more preferably from dicotyledonous plants and most preferably from plants of the family Cucurbitaceae and Cruciferae respectively, such as C. maxima and Arabidopsis thaliana, or a protein having substantial homology thereto. As used in the present application, substantial sequence homology means close structural relationship between sequences of nucleotides or amino acids. For example, substantially homologous DNA sequences may be 60 % homologous, preferably 80 % and most prefer¬ ably 90 % or 95 % homologous, or more, and substantially homologous amino acid sequences may preferably be 35 %, more preferably 50 %, most preferably more than 50 % homologous. Homology also includes a relationship wherein one or several subse¬ quences of nucleotides or amino acids are missing, or subsequences with additional nucleotides or amino acids are interdispersed. The term "homology" as used herein not only embraces structural homology but also functional homology. The invention thus further relates to a DNA sequence, which encodes a GA 20-oxidase obtainable from Cucurbita maxima or Arabidopsis thaliana or a protein having at least 35 %, preferably at least 50 %, and most preferably at least more than 50% homology therewith. More specifically, the invention relates to a DNA having a sequence corresponding to the open reading frame of the sequence shown in SEQ ID NO 1, SEQ ID NO 3 and SEQ ID NO 5, or an equivalent sequence through the degeneracy of the genetic code, including derivatives capable of hybridizing with the sequence shown in SEQ ID NO 1, SEQ ID NO 3 or SEQ ID NO 5, and still encoding a polypeptide exhibiting GA 20-oxidase activity. A preferred embodiment of the invention is therefore a substantially pure DNA as shown in SEQ ID NO 1, SEQ ID NO 3, or SEQ ID NO 5, or having substantial sequence homology to the sequence shown in SEQ ID NO 1, SEQ ID NO 3, or SEQ ID NO 5. The DNA sequence according to the invention is preferably a recombinant DNA comprising a DNA sequence which encodes a recombinant polypeptide exhibiting GA 20-oxidase activity. In one embodiment of the invention the recombinant DNA is in the form of a cDNA clone. It is a further object of the invention to provide a chimaeric gene construct comprising a DNA sequence encoding a polypeptide exhibiting GA 20-oxidase activity in operable linkage with plant expression signals including promoter and termination sequences capable of causing the gene to express a polypeptide exhibiting GA 20-oxidase activity within a plant, wherein the promoter sequences are preferably those of an inducible promoter or a tissue-preferential or a tissue-specific promoter. The invention further comprises a chimaeric gene construct comprising at least a part of a reverse GA 20-oxidase nucleotide sequence, in operable Unkage with plant expression signals including promoter and termination sequences capable of causing the reverse sequence to express antisense mRNA within a plant. It is also an object of the invention to provide transformed host cells comprising recombinant DNA encoding a polypeptide exhibiting GA 20-oxidase activity in operable linkage with expression signals including promoter and termination sequences which permit expression of said DNA in the host cell. A preferred embodiment of the invention is a transgenic plant including seed and progeny or propagules thereof comprising preferably stably integrated into its genome a chimeric gene construct as mentioned hereinbefore. Preferred is a monocotyledonous and a dicotyledonous plant, respectively such as tobacco, tomato, cotton, sunflower, maize, wheat and Dactylis glomerata. Especially preferred is a transgenic plant which is a monocotyledonous plant, preferably a maize plant or a wheat plant. The invention also comprises a recombinant polypeptide obtainable from plants or fungi exhibiting GA 20-oxidase activity, which polypeptide is preferably capable of acting essentially on one or more of the following substrates: GA- , GA53, GA15 (open or closed lactone), GA44 (open or closed lactone), GA24, GA19 and GA23. A preferred embodiment of the invention is therefore a recombinant polypeptide which exhibits a GA 20-oxidase activity and which is obtainable from plants or fungi, preferably from monocotyledonous and dicotyledonous plants, respectively, more preferably from dicotyledonous plants and most preferably from plants of the family Cucurbitaceae and Cruciferae respectively, such as C. maxima and Arabidopsis thaliana, or a protein having substantial homology thereto. More specifically, the invention relates to a recombinant polypeptide having a sequence as shown in SEQ ID NO 2, SEQ ID NO 4 AND SEQ ID NO 6, or an sequence that is substantially homolgous thereto. The invention further comprises a method of preparing a DNA sequence encoding a GA 20-oxidase, comprising preparing a cDNA library from a suitable source organism, and screening this library by means of one of the conventionally applied screening systems. The invention also comprises a method of preparing a recombinant polypeptide exhibiting GA 20-oxidase activity, which comprises of one of the DNA sequences mentioned hereinbefore. A further embodiment of the invention is a method of identifying DNA sequences comprising a DNA region encoding a polypeptide exhibiting GA 20-oxidase activity which method comprises preparing a cDNA or a genomic library from a suitable source organism and screening this library by means of hybridisation using a suitable DNA as a hybridisation probe. In the first place, the present invention relates to a DNA sequence encoding a polypeptide exhibiting GA 20-oxidase activity. Examples of a DNA sequence according to the invention are the open reading frames of the sequences shown in SEQ ID NO 1, SEQ ID NO 3 and SEQ ID NO 5 or an equivalent sequence through the degeneracy of the genetic code. Thus, a DNA sequence according to the invention may be one which codes for the amino acid sequence shown in SEQ ID NO 2, SEQ ID NO 4 and SEQ ID NO 6. It will be well understood that the invention includes derivatives and mutants of the sequences shown in SEQ ID NO 1, SEQ ID NO 3 and SEQ ID NO 5, provided that such derivatives encode essentially similar peptides having essentially the same function as the peptides encoded by the GA 20-oxidase gene described herein. The said derivatives of the DNA sequence according to the invention may be naturally occurring variants or mutants or, especially, they may be artificially created variants or mutants that may be produced specifically or unspecifically by known mutation methods. Mutation is to be understood as meaning both the deletion or insertion of one or more bases and the substitution of one or more bases, or a combination of these measures. This is the case especially when the said base substitution is accompanied by a silent mutation which does not result in amino acid substitution and thus does not change the chemical structure of the expression product The structural gene according to the invention encoding GA 20-oxidase may constitute an uninterrupted coding sequence or it may include one or more introns, bounded by the appropriate splice junctions functional in plants, which may be obtained from a synthetic or a natural source. The structural gene according to the invention encoding GA 20-oxidase may further be obtained exclusively from naturally occurring or from synthetic sources. It may be obtained, for example, from a genomic or from a cDNA library or constructed entirely by synthetic means. Another possibility is the construction of a hybrid DNA sequence comprising cDNA and also genomic DNA and/or synthetic DNA. In that case, the cDNA may originate from the same gene as the genomic DNA, or both the cDNA and the genomic DNA may originate from different gene sources. In any case, however, the genomic DNA and/or the cDNA may each be produced individually from the same gene or from different genes. If the structural gene contains portions of more than one gene, these genes may originate from one and the same organism, from several organisms belonging to different strains or varieties of the same species or different species of the same genus, or from organisms belonging to more than one genus of the same or a different taxonomic unit In any event, the DNA sequence is considered to be within the scope of the invention, if the protein encoded has a GA 20-oxidase activity. The invention also provides a method of preparing a recombinant DNA encoding GA 20-oxidase. The method may include preparing a cDNA library from a suitable source, and screening this library by means of an antibody against GA 20-oxidase or part of its amino acid sequence, or screening the library by testing for catalytic activity characteristic of the GA 20-oxidase or by any other suitable method known in the art. Standard techniques in recombinant DNA technology can be used as part of the method, such as hybridisation using cDNA probes, polymerase chain reaction using degenerate primers, and restriction fragment length polymorphism. The method of preparing a recombinant DNA encoding GA 20-oxidase may include pre¬ paring a genomic or a cDNA gene library that can be produced by customary routine methods very well known to the person skilled in that field. The basic methods of producing genomic or cDNA gene libraries are described in detail, for example, in Maniatis et al (1982), while information relating to the transfer and application of those methods to plant systems will be found, for example, in the Mohnen (1985) reference [Mohnen et al, EMBO J., 4: 1631-1635 (1985)]. Genomic DNA and cDNA can be obtained in various ways. Genomic DNA, for example, can, using known methods, be extracted from suitable cells and purified. In a specific embodiment of the present invention, the starting material used for the production of cDNA is generally mRNA, which can be isolated from selected cells or tissues, but especially from cells or tissues of immature seeds of Cucurbitaceae plants such as, for example, C. maxima, which are known to be a rich source of GA biosynthetic enzymes. A further suitable source of GA biosynthetic enzymes is the shoot tissue of Arabidopsis thaliana plants. The isolated mRNA can then be used in a reverse transcription as the matrix for the production of a corresponding cDNA. The methods of isolating poly(A + ) RNA and of producing cDN A are known to the person skilled in the art and are described in detail below in the Examples. The extracted and purified DNA preparations are then cleaved into fragments for the subsequent cloning. The genomic DNA or cDNA to be cloned may be fragmented to a size suitable for insertion into a cloning vector either by mechanical shearing or, preferably, by cleavage with suitable restriction enzymes. Suitable cloning vectors which are already being used as a matter of routine for the production of genomic and/or cDNA gene libraries include, for example, phage vectors, such as the λ Charon phages, or bacterial vectors, such as the E. coli plasmid pBR322. Further suitable cloning vectors are known to the person skilled in the art and may be obtained from commercial sources such as, for example, that contained in the 'Fast Track' mRNA isolation kit obtainable from INNTTROGEN or the λgtl 1 Cloning Kit of Amersham. From the gene libraries produced in that manner, suitable clones comprising the desired gene or parts thereof can then be identified in a screening program, for example with the aid of suitable oligonucleotide probes (probe molecule), and then isolated. Various methods are available for identifying suitable clones, for example differential colony hybridisation or plaque hybridisation. Immunological detection methods based on identification of the specific translation products may also be used. There may be used as probe molecule, for example, a DNA fragment that has already been isolated beforehand from the same gene or from a structurally related gene and that is capable of hybridisation with the corresponding section of sequence within the desired gene that is to be identified. Provided that the amino acid sequence of the gene to be isolated or at least parts of that sequence are known, a corresponding DNA sequence can be drawn up on the basis of that sequence information. On the basis of that information it is thus possible to draw up oligonucleoti.de molecules that can be used as probe molecules for the identification and isolation of suitable clones by hybridising the said probe molecules with genomic DNA or cDN A in one of the methods described above. In order to facilitate detection of the desired gene, the above-described DNA probe molecule can be labelled with a suitable readily detectable group. Within the scope of this invention, a detectable group is to be understood as being any material having a particular readily identifiable physical or chemical property. Such materials are already widely used especially in the field of immunoassays, and the majority of them may also be employed in the present Application. Special mention may be made at this point of enzymatically active groups, for example enzymes, enzyme substrates, coenzymes and enzyme inhibitors, and also of fluorescent and luminescent agents, chromophores and radioisotopes, for example, , ^S, 32 p> 125j ^ 14Q - ^ Q ready detectability of these labels is based on the one hand on their inherent physical properties (e.g. fluorescent labels, chromophores, radioisotopes) and on the other hand on their reaction and binding properties (e.g. enzymes, substrates, coenzymes, inhibitors). Also suitable as a probe molecule is a single-stranded cDNA derived from a poly(A) + RNA, which in turn is isolated from a tissue or a cell known to contain high levels of GA biosynthetic enzymes. For example, the cDNA sequence of the present invention may be used to isolate genomic or further cDNA sequences encoding GA 20-oxidase. Where a partial cDNA has been obtained, the partial cDNA may be used as a probe to screen the cDNA library in order to isolate a full length cDNA clone. Hybridizing clones are purified, restriction mapped and sequenced. A full length clone will be near message size as well as having a complete open reading frame. To isolate a genomic clone, the full length cDNA is used as a probe to screen a genomic library. By restriction mapping and hybridization to the cDNA, the coding region of the genomic clone is identified. The area upstream from the coding area of the clone is the promoter region. General methods relating to hybridisation are described, for example, in Maniatis T. et al (1982) and in Haymes B.T. et al (1985) [Haymes B.T. et al, Nucleic Acid Hybridisation: a Practical Approach, IRL Press, Oxford, England (1985)]. Those clones within the above-described gene libraries which are capable of hybridisation with a probe molecule and which can be identified by means of one of the above- mentioned detection methods can then be analysed further in order to determine in detail the extent and nature of the coding sequence. An alternative method of cloning genes is based on the construction of a gene library composed of expression vectors. In that method, analogously to the methods already described above, genomic DNA, but preferably cDNA, is first isolated from a cell or a tissue capable of expressing a desired gene product - in the present case GA 20-oxidase - and is then spliced into a suitable expression vector. The gene libraries so produced can then be screened using suitable measures, preferably using antibodies, and those clones selected which comprise the desired gene or at least part of that gene as an insert. Alternatively, total DNA from the DNA library, preferably from the cDNA library, can be prepared and used as a template for a PCR reaction with primers representing low degeneracy portions of the amino acid sequence. Preferably, the primers used will generate PCR products that represent a significant portion of the nucleotide sequence. The PCR products can be further probed to determine if they correspond to a portion of the GA 20-oxidase gene using a synthetic oligonucleotide probe corresponding to an amino acid fragment sequence located in the interior or middle region of the GA 20-oxidase protein. The cDNA clones and PCR products prepared as described above or fragments thereof may be used as a hybridization probe in a process of identifying further DNA sequences from a homologous or a heterologous source organism encoding a protein product that exhibits GA 20-oxidase activity such as, for example, a fungi or a monocotyledonous plant. A suitable source would be developing tissue from maize or wheat plants. They may also be used as a RFLP marker to determine, for example, the location of the GA-20 oxidase gene or a closely linked trait in the plant genome or for marker assisted breeding [EP-A 306,139; WO 89/07647]. Using the methods described above it is thus possible to isolate a gene that codes for a GA 20-oxidase. For further characterisation, the DNA sequences purified and isolated as described above are subjected to sequence analysis. The previously isolated DNA is first cleaved into fragments by means of suitable restriction enzymes and then cloned into suitable cloning vectors, for example the M13 vectors mp 18 and mp 19. The sequencing is carried out in the 5' to 3' direction, the dideoxynucleotide chain termination method according to Sanger [Sanger et al, 1977] or the method according to Maxam and Gilbert [Maxam and Gilbert, 1980] or a commercially available nucleotide sequencing instrumentation [available from Applied Biosystems, Foster City, California and Dupont, Wilmington, Delaware] prefer¬ ably being used. In order to avoid errors in sequencing, it is advantageous to sequence the two DNA strains in parallel. The analysis of the nucleotide sequence and of the corres¬ ponding amino acid sequence is advantageously computer-assisted using suitable commercially available computer software [e.g. GCG software of the University of Wisconsin]. The area upstream from the coding area of the clone is the promoter region. The GA 20-oxidase promoter region may be more precisely mapped through deletion analysis. 5' deletions of a GA 20-oxidase promoter are made by introducing restriction sites by PCR using oligonucleotide primers with restriction sites at the 5' ends and promoter sequences at the 3' ends. The PCR products are digested, purified, and cloned into a suitable cloning vector such as, for example, into pBHOl (Clontech). The deletion mutants contain the 5' untranslated leader sequence fused to the translational start site of the GUS gene. Internal and 3' deletions of the GA 20-oxidase promoter are made by PCR in a similar manner. The PCR fragments are fused to a GUS vector containing the CAMV 35S minimal pro¬ moter [-46 to +1; Benfey et al, 1990]. Transgenic plants are tested with the GUS fluorometric and histochemical assay. The GA 20-oxidase promoter region may be suitably used within the scope of the present invention for the preparation of recombinant, or chimaeric, DNA constructs comprising a GA 20-oxidase structural gene, which may be of homologous or of heterologous origin relative to the promoter sequence. The present invention thus further comprises recombinant DNA sequences comprising, in a 5' to 3' direction, a promoter region obtainable from a GA 20-oxidase genomic DNA sequence, which is operatively linked to a GA 20-oxidase coding DNA sequence, which may be homologous or heterologous relative to the promoter sequence. The recombinant DNA sequences result in expression of the associated homologous or heterologous GA 20-oxidase in transformed plant material. In principle, the DNA can also be prepared by chemical synthesis. In another aspect, the invention provides a recombinant polypeptide exhibiting GA 20-oxidase activity. This polypeptide or enzyme is soluble and 2-oxoglutarate-dependent. It is capable of acting on, for example, one or more of the following substrates: GAχ2 > GA53, GA15 (open or closed lactone), GA44 (open or closed lactone), GA24, GA19 and GA23. The GA 20-oxidase may be derived from plants or fungi, preferably from mono¬ cotyledonous and dicotyledonous plants respectively, and more preferably from dicotyledonous plants. A particularly suitable source is plants of the family Cucurbitaceae, such as C. maxima, of which the immature seeds are a convenient source. A further suitable source is plants of the family Cruciferae, such as Arabidopsis thaliana, of which shoot material is a convenient source. In particular, the recombinant GA 20-oxidase is derived from C. maxima or Arabidopsis thaliana respectively, or is a protein having substantial homology thereto (as defined above). An embodiment of this latter aspect of the invention is a GA 20-oxidase having the amino acid sequence shown in SEQ ID NO 2, SEQ ID NO 4 and SEQ ID NO 6. The invention also includes a protein having substantial homology (as defined above) with this amino acid sequence and having GA 20-oxidase activity. Modified proteins derived from this amino acid sequence by mutation, i.e. addition, substitution or deletion of one or more amino acid residues, and having GA 20-oxidase activity, are also included within the scope of the invention. Once having identified and isolated the DNA encoding a polypeptide product exhibiting GA 20-oxidase activity, a purified protein can be obtained from transgenic expression of the said DNA, i.e., placing a recombinant DNA comprising a DNA sequence coding for a protein exhibiting GA 20-oxidase activity into an appropriate bacterial, yeast, plant or other suitable cell expression system. Suitable hosts include bacteria such as E. coli and yeast, including the strain Saccharomyces cerevisiae. Other suitable expression system hosts include insect cells grown in culture. These insect cells may be infected with a baculovirus containing a recombinant DNA molecule according to the invention. Alternatively, the baculovirus may be used to infect the cells of a living insect, and the insect cells used as the expression system host. The expression system host is then allowed to produce an expression supernatant. This allows facile generation of large amounts of purified recombinant GA 20-oxidase by isolating the enzyme from the expression supernatant. A further object of the present invention is chimaeric gene constructions comprising, in addition to the DNA sequence according to the invention encoding GA 20-oxidase, expression signals which include both promoter and terminator sequences and other regulatory sequences of the 3' and 5' untranslated regions and which are operably linked to the coding DNA sequence such as to ensure the expression of the corresponding gene product in the respective host organism. Suitable control sequences that are preferred within the scope of the invention are those comprising promoter and 5' and 3' untranslated regulatory sequences that are functional in plants. These sequences may, independently, be derived from any source, such as, for example, virus, plant or bacterial genes. These promoters or regulatory sequences can be constitutive in nature or can be regulated in their patterns of expression. Such regulation may be temporal or spatial and include developmentally regulated promoters and inducible promoters. Proteins may be optionally expressed in the vacuole or extracellularly using methods well-known in the art (EP 462,065). In general, any promoter and any terminator capable of bringing about an induction of the expression of a coding DNA sequence (structural gene) may be used as a constituent of the chimaeric gene sequence according to the invention. The said expression signals may promote continuous and stable expression of the gene. Especially suitable are expression signals originating from genes of plants or plant viruses. Examples of suitable promoters and terminators are those of the Cauliflower Mosaic Virus genes (CaMV) or homologous DNA sequences that still have the chacteristics properties of the mentioned expression signals. Also suitable are bacterial expression signals, especially the expression signals of the nopaline synthase genes (nos) or the opine synthase genes (ocs) from the Ti-plasmids of Agrobacterium tumefaciens. Also to be mentioned here are, for example, ubiquitine promoters, actin promoters, histone promoters and tubulin promoters. Other suitable promoters are an amylase promoter (a-amylase promoter) and an ABA (abscisic acid) inducible promoter. In a further embodiment of the invention a promoter region may be used that is obtainable from a GA 20-oxidase genomic DNA sequence as described hereinbefore. Within the scope of this invention, preference is given to the 35S and 19S expression signals of the CaMV genome or their homologues which can be isolated from the said genome using molecular biological methods, as described, for example, in Maniatis et al (1982), and linked to the coding DNA sequence. Further preferred are expression signals that comprise tissue-preferential or tissue-specific promoters. The term tissue-preferential promoter is used to indicate that a given expression signal will promote a higher level of transcription of an associated expressible DNA, or of expression of the product of the said DNA as indicated by any conventional RNA or protein assay, or that a given DNA sequence will demonstrate some differential effect; i.e., that the transcription of the associated DNA sequences or the expression of a gene product is greater in some tissue than in all other tissues of the plant. For example, the tissue-preferential promoter may direct higher expression of an associated gene product in leaves, stems, roots and/or pollen than in seed. One example of a tissue-preferential promoter, which may be suitably used within the scope of the present invention, is a pith-preferred promoter isolated from a maize TrpA gene. The term tissue-specific promoter is used to indicate that a given regulatory DNA sequence will promote transcription of an associated expressible DNA sequence entirely in one or more tissues of a plant, or in one type of tissue, while essentially no transcription of that associated coding DNA sequence will occur in all other tissues or types of tissues of the plant Numerous promoters whose expression are known to vary in a tissue specific manner are known in the art. One such example is the maize phosphoenol pyruvate car- boxylase [PEPC], which is green tissue-specific [Hudspeth R.L. and Grula J.W., 1989]. Other green tissue-specific promoters include chlorophyll a/b binding protein promoters and RubisCo small subunit promoters. Further to be mentioned here are, for example, pollen-specific promoters such as those obtainable from a plant calcium-dependent phosphate kinase [CDPK] gene. A developmentally regulated promoter can also be used. Of course, in the present invention, any promoter which is functional in the desired host plant can be used to direct the expression of an associated gene. In general, the GA 20-oxidase structural gene may be linked to the promoter region in either a sense or an anti-sense orientation. It is often advantageous to incorporate a leader sequence between the promoter sequence and the adjacent coding DNA sequence, the length of the leader sequence being so selected that the distance between the promoter and the DNA sequence according to the invention is the optimum distance for expression of the associated structural gene. Suitable leader sequences include leader sequences of various lengths isolated from the 35S CaMV gene (Pierce et al., 1987). The preferred leader sequences are those isolated from the 35S CaMV gene, having a length from about 50 to about 130 nucleotides. The identification of other leader sequences is known in the art. See Della-Cioppa et al, 1987; Schekman, 1985. Further regulatory DNA sequences that may be used for the construction of chimaeric genes include, for example, sequences that are capable of regulating the transcription of an associated DNA sequence in plant tissues in the sense of induction or repression. There are, for example, certain plant genes that are known to be induced by various internal and external factors, such as plant hormones, heat shock, chemicals, pathogens, oxygen deficiency, light, stress, etc. Another class of genes that are suitable in plants comprises the light-regulated genes, especially the nuclear-coded gene of the small subunit of ribulose-l,5-biphosphate carboxylase (RUBISCO). Morelli et al (1985) have shown that the 5 '-flanking sequence of a RUBISCO gene from the pea is capable of transferring light-inducibility to a reporter gene, provided the latter is linked in chimaeric form to that sequence. It has also been possible to extend this observation to other light-induced genes, for example the chlorophyll-a/b-binding protein. A further group of regulatable DNA sequences comprises chemically regulatable sequen¬ ces that are present, for example, in the PR (pathogenesis-related) protein genes of tobacco and are inducible by means of chemical regulators such as those described in EP-A-332,104. In a specific embodiment of the invention a promoter of the Arabidopsis PR la gene is being used. The regulatable DNA sequences mentioned by way of example above may be of both natural and synthetic origin, or they may comprise a mixture of natural and synthetic DNA sequences. The recombinant DNA sequences of the present invention may further comprise a signal sequence, which is operatively linked to the coding DNA sequence. The signal sequence is responsible for specialized transport of the associated peptide within the plant cell. The signal sequence of the present invention may be any DNA sequence which is able to direct the transport of an associated polypeptide into one or more of the cellular compartments. The signal sequence is preferably a sequence which is translated into a signal peptide, which becomes separated from the peptide after transit of the peptide is complete. Signal sequences are useful for directing the polypeptide product of the coding DNA sequence to a desired location within the cell, such as to the mitochondria or to the endoplasmic reticulum, or to direct extracellular transport outside of the cell. To be mentioned here are, for example, N-terminal signal peptides, which are involved in intracellular transport and which can be found at the N-terminal end of proteins transported via the endomembrane system. These signal sequences ensure that the said proteins first pass into the endoplasmic reticulum, where the signal peptide is split off proteolytically from the precursor protein as soon as it has fulfilled its function. By virtue of its specific function, this type of signal peptide sequence has been conserved to a high degree during evolution in all living cells, irrespective of whether they are bacteria, yeasts, fungi, animals or plants. At the C-terminal end of vacuolar proteins, on the other side, sequences may be found that are involved in directing the expression of the associated coding part of the plant vacuole. Examples of these so-called 'vacuolar targeting' sequences are provided, for example, in EP-A 462,065. Moreover, the DNA molecule may comprise further sections of sequence that code for peptide fragments which as a whole contribute towards improving the competence for admission into the vacuole, for example the propeptide fragment discovered by Matsuoka K. and Nakamura K. in the N-terminal extension of sporamine [Matsuoka K. and Nakamura K. (1991)]. Further signal sequences useful for the present invention are, for example, the signal sequence from the pathogenesis-related gene (PR-1) of tobacco, which is described in Cornellisen et al, 1986; the yeast mitochondrial presequence; Schmitz et al, 1989; the signal sequence from plant mitochondrial Rieske iron-sulfur protein, Huang et al, 1991; mitochondrial and chloroplast targeting peptides, von Heijne etal, 1989. The present invention therefore also includes chimaeric genetic constructions that comprise, in operable linkage with a structural gene encoding GA 20-oxidase, further regulatory sections of DNA sequence permitting, for example, specifically controlled induction or repression of gene expression. As a modification of the above aspect, the invention also provides a chimaeric gene construct comprising at least a part of a reverse GA 20-oxidase nucleotide sequence, having at its 5 '-end a promoter capable of causing the reverse sequence to express antisense mRNA within a plant and, optionally, further regulatory DNA sequences such as those mentioned above. The various sections of the chimaeric DNA sequences according to the invention may be linked to one another by methods known per se to form a complete coding DNA sequence. Suitable methods include, for example, the in vivo recombination of DNA sequences having homologous sections and the in vitro linking of restriction fragments. In the above in vivo and/or in vitro processes for assembling the different sections of the said functional unit, cloning vectors may be involved such as, for example, plasmid or virus (bacteriophage) vectors having replication and control sequences originating from species that are compatible with specific host cells. The cloning vector generally carries an origin of replication, especially an origin of replication that is capable of functioning in E. coli, in Agrobacterium or in both, and, in addition, specific genes that lead to phenotypic selection features in the transformed host cell, especially to resistance to antibiotics or to specific herbicides. The transformed vectors can be selected on the basis of those phenotypic markers after transformation in a host cell. The cloning vectors and the host cell transformed with those vectors are generally used to increase the number of copies of the constructs cloned therein. With an increased number of copies it is possible to isolate the vector carrying the chimaeric gene construction and prepare it, for example, for insertion of the chimaeric gene sequence into a plant cell. Especially suitable within the scope of the present invention are so-called shuttle vectors, which can stably replicate not only in one but in at least two different host organisms such as, for example, in E. coli and in Agrobacterium tumefaciens, in the presence of a suitable selection marker. Selectable phenotypic markers that may be used within the scope of this invention include, for example, resistance to ampicillin, tetracycline, hygromycin, kanamycin, methotrexate, G418 and neomycin, but this list, which is given by way of example, is not intended to limit the subject of the invention. Suitable host cells within the scope of this invention are prokaryotes, including bacterial hosts, for example A. tumefaciens, E. coli, S. typhimurium and Serratia marcescens, and also cyanobacteria. Eukaryotic hosts, such as yeasts, mycelium-forming fungi and plant cells, may also be used within the scope of this invention. The splicing of the chimaeric gene construction according to the invention into a suitable cloning vector is carried out using standard methods, such as those described, for example, in Maniatis et al (1982) and Sambrook et al (1989). In a further process step, the cloned structural gene coding for GA 20-oxidase may be introduced into one of the commonly used plant transformation cassettes and transformed into a plant cell using standard techniques and, optionally, integrated into the plant genome. The detection of transformed plant cell may be accomplished using suitable selection systems. Very convenient selection systems that are preferably applied in transient expression systems are those that are based on a scorable marker such as, for example, regulatory or structural genes controlling anthocyanin biosynthesis, GUS (β-glucuronidase), lucif erase, opine synthetases, thaumatin, β-galactosidase, unique synthetic epitopes designed for easy detection by ELIS A, phycobiliproteins and various fluorogenic substances. In a specific embodiment of the present invention use is made of the 'GUS '-based marker system, which involves a DNA sequence encoding a β-glucuronidase enzyme operably linked with one or more of the expression signals listed above. Upon expression of the GUS gene in the plant cell the β-glucuronidase enzyme may react with its specific substrate, which leads to the appearance of blue spots that can be easily detected in the plant tissue. In a further embodiment of the present invention the use is made of coding sequences for the anthocyanin regulatory genes known in the art as Cl and B-Peru [Goff et al, 1990]. Such coding sequences, operably linked to one or more of the several constitutive promoters listed above, can be used to isolate transformants on the basis of the red pigmentation of cells transformed with such genes. The 'anthocyanin '-based marker system, on the other hand, involves a red colour reaction. In a further aspect, the invention provides a transformed host cell comprising recombinant DNA encoding a polypeptide exhibiting GA 20-oxidase activity in operable linkage with expression signals including promoter and termination sequences which permit expression of said DNA in the host cell. Where the host cell is a plant cell, transgenic plants can be obtained. Thus, the invention provides for the first time a transgenic plant with an altered GA biosynthetic pathway, in particular one which contains and is capable of expressing a recombinant GA:2-oxoglutarate dioxygenase gene. Thus, there is provided a transgenic plant comprising a recombinant DNA encoding a polypeptide exhibiting GA 20-oxidase activity in operable linkage with plant expression signals including promoter and termination sequences which permit expression of said DNA in the plant. A modification of the above aspect of the invention is the transformation of a plant with a construct containing a reverse GA 20-oxidase nucleotide sequence (the entire coding sequence or a part thereof) for transcription of antisense mRNA and consequent reduced expression of the GA 20-oxidase gene. Examples of antisense technology are provided in EP-A 240 208 (Calgene) and EP-A 458 367 (Calgene). The reverse nucleotide sequence may be in association with a promoter which is specific to certain plant tissues and/or to external stimulus (e.g. light, cold, heat, chemicals etc.). Another possible means of reducing expression is for example the use of ribozyme technology as described in EP-A 321 201 or WO 89/05852. A combination of antisense and ribozyme technology may also be used within the scope of the present invention for regulating GA 20-oxidase activity. Also an overexpression of the GA 20-oxidase gene in plants may result in reduced levels of biologically acitve gibberellins in plants. The invention includes progeny or propagules, including seed, of transgenic plants as defined above. The invention also includes methods of making such transgenic plants. The recombinant DNA according to the invention comprising the GA 20-oxidase encoding DNA sequence can be introduced into the plant cell in a number of ways that are well known to those of skill in the art. For example, methods of transforming plant cells include microinjection [Crossway et al (1986); Neuhaus (1987)], electroporation [Riggs et al (1986)], Agrobacterium mediated transformation [Hinchee et al (1988)], direct gene transfer [Paszkowski et al, (1984)], and ballistic particle acceleration using, for example, devices available from Agracetus, Inc., Madison, Wisconsin and Dupont, Inc., Wilmington, Delaware [see, for example, Sanford et al, U.S. Patent 4,945,050; and McCabe et al, (1988). Also see, Weissinger et al (1988); Sanford et al (1987) (onion); Christou et al (1988) (soybean); McCabe et al (1988) (soybean); Datta et al (1990) (rice); Klein et al (1988) (maize); Klein et al (1988) (maize); Klein et al (1989) (maize); Fromm et al (1990); Gordon-Kamm etal (1990) (maize)]. One possible method for introducing genetic material into plant cells comprises, for example, bringing plant cells into contact with viruses or with Agrobacterium comprising the DNA to be introduced. This may be achieved by infecting sensitive plant cells or by co-cultivating protoplasts derived from plant cells. Within the scope of this invention, Cauliflower Mosaic Virus (CaMV) may be used as a vector for the insertion of the GA 20-oxidase-encoding DNA sequence according to the invention into a plant. Another metiiod of inserting GA 20-oxidase-encoding DNA sequence into a cell makes use of die infection of die plant cell witi Agrobacterium tumefaciens and/or Agro¬ bacterium rhizogenes, which has previously been transformed witii die said gene con¬ struction. The transgenic plant cells are then cultured under suitable culture conditions known to die person skilled in the art, so tiiat they form shoots and roots and whole plants are finally formed. A further possible metiiod of transforming plant material comprises mixed infection using both Agrobacterium rhizogenes and transformed Agrobacterium tumefaciens, as described by Petit et al (1986) for die transformation of carrots. The GA 20-oxidase-encoding DNA sequence according to the invention can tiierefore be transferred into suitable plant cells by means of, for example, die Ti-plasmid of Agrobacterium tumefaciens or the Ri-plasmid of Agrobacterium rhizogenes. The Ti-plas¬ mid or Ri-plasmid is transferred to the plant in die course of infection by Agrobacterium and integrated in stable manner into die plant genome. Any T-DNA-containing vector that can be transferred into plant cells and permits selection of d e transformed cells is suitable for use within the scope of tiiis invention such as, for example, a shutde vector that comprises die GA 20-oxidase-encoding DNA sequence according to the invention cloned in between the left border sequence (LB) and the right border sequence (RB) and that is capable of stable replication botii in E. coli and in A. tumefaciens. Preferred is a so-called binary vector system. Using newly developed transformation techniques, it has also become possible in principle to transform in vitro plant species that are not natural host plants for Agrobacterium. For example, monocotyledonous plants, especially the cereal species and various grasses, are not natural hosts for Agrobacterium. It has become increasingly evident that monocotyledons can also be transformed using Agrobacterium, so tiiat, using new experimental formulations mat are now becoming available, cereals and grass species are also amenable to transformation [Grimsley N.H. et al (1987)]. One of the preferred methods for introducing DNA into a plant cell by means of Agro¬ bacterium is the so-called leaf disk transformation using Agrobacterium [Horsch et al (1985)]. Sterile leaf disks from a suitable target plant are incubated with Agrobacterium cells comprising one of the GA 20-oxidase-encoding DNA sequence according to the invention, and are tiien transferred into or onto a suitable nutrient medium. Especially suitable, and tiierefore preferred within die scope of tiiis invention, are LS media that have been solidified by die addition of agar and enriched witii one or more of die plant growtii regulators customarily used, especially those selected from the group of die auxins consisting of a-naphdiylacetic acid, picloram, 2J *-trichlorophenoxyacetic acid, 2,4 lorophenoxyacetic acid. iole-3 utyric ac _ iole-3-la-r acid, indo' p -3- sue z acid, indole-3-acetic ac * i p-c i τopheno> z acid, a- " • m the gr - the okinins consisting of ki: , 6-foι. zyladenine openteny sine and Zl. The ^referred concentration of a uns and cytokinins .< the range rom 0.1 γ to lO mg/1. After incubation for several days but preferably after incubation for 2 to 3 days at a temperature of from 20C to 40C, preferably from 23C to 35C and more especially at 25C and in diffuse light, the leaf disks are transferred tc • table medium for the purpc^ of shoot induction. Especially preferred for the selec o ~ of the transformants is S medium that does not c ntain auxin but contain Jrinin instead, and to ^ -i a selective substance has been added dependent on the marker gene used. The cult. _s are kept in the light and are transferred to fresh medium at suitable intervals, but preferably at intervals of one week. Developing green shoots are cut out and cultured further in a medium that induces die shoots to form roots. Especially preferred within the scope of tiiis invention is an LS medium tiiat does not contain auxin or cytokinin but to which a selective substance has been added for the selection of the transformants. In addition to Agrobacterium-τaediaxed transformation, widiin die scope of tiiis invention it is possible to use direct transformation methods for the insertion of die gene constructions according to the invention into plant material. Possible methods for me direct transfer of genetic material into a plant cell comprise, for example, the treatment of protoplasts using procedures that modify die plasma membrane, for example, polyethylene glycol treatment, heat shock treatment or electroporation, or a combination of those procedures [Shillito et al (1985)]. In the electroporation technique, plant protoplasts together witii plasmids that comprise the GA 20-oxidase-encoding DNA sequence are subjected to electrical pulses of high field strength. This results in a reversible increase in the permeability of biomembranes and thus allows the insertion of the plasmids. Electroporated plant protoplasts renew their cell wall, divide and form callus tissue. Selection of the transformed plant cells can take place with die aid of the above-described phenotypic markers. A further method for the direct introduction of genetic material into plant cells, which is based on purely chemical procedures and which enables the transformation to be carried out very efficiently and rapidly, is described in Negrutiu I. et al (1987). Also suitable for die transformation of plant material is direct gene transfer using co-transformation (Schocher R.J. et al 1986). Co-transformation is a method that is based on die simultaneous taking up and integration of various DNA molecules (non-selectable and selectable genes) into the plant genome and mat tiierefore allows the detection of cells tiiat have been transformed with non-selectable genes. Further means for inserting genetic material contained in a vector direcdy into a plant cell comprise using purely physical procedures, for example by microinjection using finely drawn micropipettes [Neuhaus et al (1987)] or by bombarding the cells with micro- projectiles that are coated with the transforming DNA ["Microprojectile Bombardment"; Wang Y-C et al (1988)] or are accelerated through a DNA containing solution in the direction of the cells to be transformed by a pressure impact thereby being finely atomized into a fog with die solution as a result of the pressure impact [EP-A-434,616]. Microprojectile bombardment has been advanced as an effective transformation technique for cells, including cells of plants. In Sanford et al (1987) it was reported that microprojectile bombardment was effective to deliver nucleic acid into die cytoplasm of plant cells of Allium cepa (onion). Christou et al (1988) reported the stable transformation of soybean callus with a kanamycin resistance gene via microprojectile bombardment Christou et al reported penetration at approximately 0.1 % to 5 % of cells. Christou further reported observable levels of NPTII enzyme activity and resistance in the transformed calli of up to 400 mg/1 of kanamycin. McCabe et al (1988) report the stable transformation of Glycine max (soybean) using microprojectile bombardment. McCabe et al further report die recovery of a transformed R plant from an R Q chimaeric plant. The transformation of maize plants, including elite maize plants, by microprojectile bombardment can be carried out according to die general protocol described for example in EP-A 478 502, the disclosure of which is incorporated herein by reference. The list of possible transformation methods given above by way of example is not claimed to be complete and is not intended to limit the subject of the invention in any way. The present invention tiierefore also comprises transgenic plant material, selected from the group consisting of protoplasts, cells, calli, tissues, organs, seeds, embryos, ovules, zygotes, etc. and especially, whole and preferably phenotypically normal plants, that has been transformed by means of die processes described above and comprises the recombinant DNA according to the invention in expressible form, and processes for the production of die said transgenic plant material. Preferred within the present invention are monocotyledonous plants including seed and the progeny or propagueles diereof, but especially graminaceous monocots such as, for example, Lolium, Zea, Triticum, Triticale, Sorghum, Saccharum, Bromus, Oryzae, Avena, Hordeum, Secale and Setaria. Especially preferred are transgenic maize, wheat, and barley plants and seed thereof. Most preferred is the Zea mays Elite inbred line Funk 2717. Screening of plant cells, tissue and plants for the presence of specific DNA sequences may be performed by Southern analysis (Soutiiern, 1975). Details of this procedure are given in Maniatis et al (1982). This screening may also be performed by the use of Polymerase Chain Reaction procedures (PCR). PCR procedures are described in detail in Mullis et al (1987) and EhrlichA(1989). Transformation of the plant cells includes separating transformed cells from those that have not been transformed. One convenient method for such separation or selection is to incorporate into the material to be inserted into the transformed cell a gene for a selection marker. As a result only those cells that have been successfully transformed will contain the marker gene. The translation product of die marker gene will then confer a phenotypic trait that will make selection possible. Usually die phenotypic trait is the ability to survive in the presence of some chemical agent, such as an antibiotic, e.g., kanamycin, G418, paromomycin, etc., which is placed in a selection media. Some examples of genes that confer antibiotic resistance include, for example, those coding for neomycin phosphotransferase kanamycin resistance, [Velten et al (1984)]; hygromycin phosphotransferase (hygromycin resistance, [van den Elzen et al (1985)], the kanamycin resistance (NPT II) gene derived from Tn5 Bevan et al (1983); [McBride et al (1990)], the PAT gene described in Thompson et al (1987), and chloramphenicol acetyl- transferase. An example of a gene useful primarily as a screenable marker in tissue culture for identification of plant cells containing genetically engineered vectors is a gene that encodes an enzyme producing a chromogenic product. One example is the gene coding for production of β-glucuronidase (GUS). This enzyme is widely used and its preparation and use is described in Jefferson (1987). Once the transformed plant cells have been cultured on tiie selection media, surviving cells are selected for further study and manipulation. Selection metiiods and materials are well known to those of skill in die art, allowing one to choose surviving cells with a high degree of predictability that die chosen cells will have been successfully transformed with exogenous DNA. After transformation of the plant cell or plant using, for example, the Agrobacterium Ti-plasmid, those plant cells or plants transformed by the Ti-plasmid so that die enzyme is expressed, can be selected by an appropriate phenotypic marker. These phenotypical markers include, but are not limited to, antibiotic resistance. Other phenotypic markers are known in the art and may be used in this invention. Positive clones are regenerated following procedures well-known in the art. Subsequendy transformed plants are evaluated for the presence of die desired properties and/or the extent to which the desired properties are expressed. A first evaluation may include, for example, the level of bacterial/fungal resistance of the transformed plants, stable heritability of the desired properties, field trials and the like. The process for the production of transformed plant material, including whole plants, thus essentially comprises: first isolating from a suitable source or synthesising by means of known processes a DNA sequence encoding a protein exhibiting GA 20-oxidase activity; operably linking the said DNA sequence in a 5' to 3' direction to plant expression sequences as defined hereinbefore; transforming the construct of step (b) into plant material by means of known processes and expressing it therein; screening of the plant material treated according to step (c) for the presence of a DNA sequence encoding a protein exhibiting GA 20-oxidase activity; and optionally regenerating die plant material transformed according to step (c) to a whole and preferably phenotypically normal plant. The present invention tiius also comprises transgenic plants and the sexual and/or asexual progeny thereof, which have been transformed with a recombinant DNA sequence according to the invention. The expression "asexual or sexual progeny of transgenic plants" includes by definition according to the invention all mutants and variants obtainable by means of known processes, such as for example cell fusion or mutant selection and which still exhibit the characteristic properties of the initial transformed plant, together with all crossing and fusion products of die transformed plant material. Another object of die invention concerns the proliferation material of transgenic plants. The proliferation material of transgenic plants is defined relative to the invention as any plant material that may be propagated sexually in vivo or in vitro. Particularly preferred within the scope of the present invention are protoplasts, cells, calli, tissues, organs, seeds, embryos, egg cells, zygotes, together with any other propagating material obtained from transgenic plants. A further aspect of the invention is the provision of an antibody raised against at least a part of the amino acid sequence of GA 20-oxidase. Such antibody is useful in screening a cDNA library in suitable vectors derived from plant tissue RNA. The GA 20-oxidase gene according to the invention is useful in the modification of growth and developmental processes in transgenic plants. For example, reduced expression with antisense RNA may result in low GA production and therefore decreased elongation growth. The 20-oxidase is a regulatory enzyme and GA production may be particularly sensitive to its activity. It is known to be regulated by day lengtii in long-day rosette plants, such as spinach, in which increased 20-oxidase activity in long days is responsible for bolting. Modifying the expression of this gene may therefore be of particular benefit. Other GA-regulated processes that are potential targets for manipulation are seed germination, flower initiation and development, fruit set and growth and sex expression in some dioecious species. Thus, in one aspect of the use of tiiis invention, reverse 20-oxidase nucleotide sequences and tissue and/or stimulus (e.g. light, heat, cold, chemical etc.)-specific promoters are used for transformation of plants so as to transcribe antisense mRNA, resulting in reduced ex¬ pression of the 20-oxidase gene. This method produces plants with reduced endogenous GA levels and consequently altered growth habit and/or otiier developmental processes. This method can be used to reduce vegetative growth as in: straw strengthening in small grain cereals and rice; for the prevention of lodging; preventing lodging in oilseed rape and improving its canopy structure; improving seedling quality for transplantation; reducing growth of turf and amenity grasses; reducing shoot growth in orchard and amenity trees; producing ornamental plants with more compact growth habits; improving tolerance to cold, drought and fungal infection; and increasing yields by diversion of assimilates from vegetative to reproductive organs. The method is also useful to prevent bolting and flowering in rosette plants, e.g. sugar beet lettuce, spinach and brassicas. It is useful to prevent sprouting, as in potato tubers. It is also useful to prevent precocious seed germination. The invention is also useful in the transformation of plants with constructs containing the 20-oxidase sequence and tissue and/or stimulus-specific promoters for increased expression of the GA 20-oxidase gene. This method will increase the levels of biologically active GAs and so modify plant development, in cases where 20-oxidation is a rate- limiting step. The method can be used to improve fruit-set and growth as in: increasing berry size in seedless grapes (also to increase rachis length and produce a less compact cluster); increasing fruit set in citrus, particularly in Clementines; delaying ripening in citrus; improving fruit set in pear and to decrease seed number, and to modify shape of apple fruit and improve skin texture. The method can potentially be used to increase stem extension and leaf expansion, for example to increase stem lengti and sugar yield in sugar cane; to increase yield and earliness in celery and rhubarb; to increase yield in cabbage, lettuce, spinach etc.; and to increase forage yields in grasslands. The method can be used to stimulate seed germination, for example in die advancement of malting and increase in malt yields in cereals (e.g. barley, wheat, oats). The method can be used to produce uniform bolting and to stimulate flowering, for example in seed production in lettuce and otiier rosette species, or in advanced cropping of artichokes. The med od can be used to induce flower formation in conifers. It can also be used to overcome dormancy of tubers and to hasten shoot emergence as in potatoes, sweet yams etc. Furthermore, the mediod can be used to induce staminate flowers in gynoecious species, such as cucumber. Reference is now made to the accompanying sequence listing and the drawings, in which: SEQ ID NO 1 shows die nucleotide sequence of GA 20-oxidase cDNA clone pBll obtained from Curcubita maxima seed. SEQ ID NO 2 shows the amino acid sequence of the GA 20-oxidase protein corresponding to cDNA clone pBll. SEQ ID NO 3 shows the nucleotide sequence of GA 20-oxidase cDNA clone pAt2301 obtained from Arabidopsis thaliana. SEQ ID NO 4 shows the amino acid sequence of the GA 20-oxidase protein corresponding to cDNA clone pAT2301. SEQ ID NO 5 shows d e nucleotide sequence of GA 20-oxidase cDNA clone pAt2353 obtained from Arabidopsis thaliana. SEQ ID NO 6 shows the amino acid sequence of die GA 20-oxidase protein corresponding to cDNA clone pAt2353 SEQ ID NO 7 shows the amino acid sequence of a synthetic peptide tiiat had been produced on the basis of the amino acid sequence of a peptide resulting from trypsin digestion of purified GAj220-oxidase from C. maxima endosperm. SEQ ID NOs 8 and 9 show the amino acid sequence of two peptides corresponding to oligodeoxynucleotide primers that are designed based on amino acid regions conserved between the Cucurbita maxima cotyledon gibberellin 20-oxidase and other plant dioxygenases, including the tomato E8 ripening-related protein, tomato ethylene-froming enzyme, hyoscamine 6-hydroxylase from Hyoscyamus niger, barley flavanone 3-hydroxylase and the A2 gene from maize. SEQ ID NOs 10 and 11 show the sequence of two oligodeoxynucleotide primers that are designed based on amino acid regions conserved between the Cucurbita maxima cotyledon gibberellin 20-oxidase and other plant dioxygenases, including the tomato E8 ripening-related protein, tomato ediylene-froming enzyme, hyoscamine 6-hydroxylase from Hyoscyamus niger, barley flavanone 3-hydroxylase and the A2 gene from maize. The upstream and downstream primers contained restriction endonuclease cleavage sites for Hindm and EcoRI, respectively, at their 5 1 termini. SEQ ID NOs 12 and 13 show the nucleotide and the corresponding amino acid sequence of an insert of cDNA clone pAt2204, whose predicted amino acid sequence is 67% identical to that of pumpkin gibberellin 20-oxidase. SEQ ID NOs 14 to 17 show the nucleotide sequences of four oligonucleotides, which are used in conjunction with the M13 universal sequencing primer in PCR reactions. Figure 1 shows the structure of GAs discussed in the application and their metabolic relationships; Figure 2 shows the metabolism of [ ΛU] GAs by C. maxima poly (A) + RNA in vitro translation products (A) or by recombinant bacteriophage plaques (B); and The invention is further illustrated by the following Examples. In the Examples, the isolation and nucleotide sequence of a cDNA clone for GAχ2 20- oxidase selected with a specific antibody from a λgtll library derived from immature Cucurbita maxima (pumpkin) cotyledons are described. The identity of the cloned gene is confirmed by expression in Escherichia coli of a functional recombinant protein, which catalyses the three-step oxidation of GAj2 to GA25 and of GA53 to GA17, as well as the formation in low yields of C19-GAS. Furthermore, 20-oxidase activity in individual bacteriophage plaques can be detected. The demonstration of 20-oxidase activity in individual bacteriophage plaques suggests that, in the absence of a suitable antibody, a functional screen of the λgtl 1 library based on measurement of enzyme catalytic activity would be successful. It will be possible to follow enzyme activity through sub-divisions of ti e library and then to select individual lysogenic colonies or plaques. Indeed, a low level of 20-oxidase activity in lysogens prepared using 3.6 x 10' pfu from the amplified library can be detected. The Examples further describe the preparation of chimeric DNA constructs comprising the GA 20-oxidase cNDA in sense and antisense orientation, which are suitable to be transformed and expressed in plants. The Examples also describe the transformation of plants with die said chimeric constructs selected from the group consisting of tobacco, carrot, sunflower, tomato, cotton, Zea mays, Dactylis glomerata and wheat. Further, in the Examples, die isolation of three additional cDNA clones [pAT2301; pAT2353; pYAP169] for GA1220- oxidase from a λgtl 1 library derived from shoot tissue of the Arabidopsis thaliana gal mutant are described. The nucleotide and amino acid sequences respectively of cDNA clones pAT2301 and pAT2353 are shown in SEQ ID NO 1 to 6. The Examples further describe the preparation of chimeric DNA constructs comprising the GA 20-oxidase cNDAs [AT2301; AT2353; YAP169] in sense and antisense orientation, which are suitable to be transformed and expressed in Arabidopsis thaliana plants and also the transformation of Arabidopsis thaliana with the said chimeric constructs. REFERENCE EXAMPLE General recombinant DNA techniques Since many of the recombinant DNA techniques employed in this invention are a matter of routine for the person skilled in the art, it is better to give a short description of these generally used techniques here rather than to describe them every time tiiey occur. Except where there is a specific indication to the contrary, all these procedures are described in the Maniatis et al (1982) reference. A. Cleaving with restriction endonucleases A reaction batch typically contains about 50 to 500 mg ml of DNA in the buffer solution recommended by the manufacturer, New England Biolabs, Beverly, MA. 2 to 5 Units of endonucleases are added for each mg of DNA and the reaction batch is incubated for from one to three hours at the temperature recommended by the manufacturer. The reaction is terminated by heating at 65C for 10 minutes or by extraction with phenol, followed by precipitation of the DNA with ethanol. This technique is also described on pages 104 to 106 of the Maniatis et al (1982) reference. B. Treatment of DNA with polymerase in order to produce blunt ends 50 to 500 mg/ml of DNA fragments are added to a reaction batch in the buffer recom¬ mended by the manufacturer, New England Biolabs. The reaction batch contains all four deoxynucleotide triphosphates in concentrations of 0.2 mM. The reaction takes place over a period of 30 minutes at 15C and is then terminated by heating at 65C for 10 minutes. For fragments obtained by cleaving with restriction endonucleases that produce 5 '-projecting ends, such as EcoRI and BamHI, the large fragment, or Klenow fragment, of DNA poly¬ merase is used. For fragments obtained by means of endonucleases that produce 3 '-projec¬ ting ends, such as PstI and Sad, the T4 DNA polymerase is used. The use of these two enzymes is described on pages 113 to 121 of the Maniatis et al (1982) reference. C. Agarose gel electrophoresis and purification of DNA fragments from gels Agarose gel electrophoresis is carried out in a horizontal apparatus, as described on pages 150 to 163 of the Maniatis et al reference. The buffer used is the tris-borate buffer described therein. The DNA fragments are stained using 0.5 mg/ml of etiiidium bromide which is either present in the gel of tank buffer during electrophoresis or is added after electrophoresis. The DNA is made visible by illumination with long-wave ultraviolet light If the fragments are to be separated from the gel, an agarose is used that gels at low temperature and is obtainable from Sigma Chemical, St. Louis, Missouri. After the electrophoresis, the desired fragment is cut out, placed in a plastics test tube, heated at 65C for about 15 minutes, extracted three times witii phenol and precipitated twice with ethanol. This procedure is slightly different from that described by Maniatis et al (1982) on page 170. As an alternative, the DNA can be isolated from the agarose witii the aid of the Geneclean kit (Bio 101 Inc., La Jolla, CA, USA). D. Addition of synthetic linker fragments to DNA ends If it is desired to add a new endonuclease cleavage site to the end of a DNA molecule, the molecule is optionally first treated with DNA-polymerase in order to produce blunt ends, as described in the section above. About 0.1 to l.OAmg of this fragment is added to about 10 ng of phosphorylated linker DNA, obtained from New England Biolabs, in a volume of 20 to 30 ml with 2ml of T4 DNA ligase from New England Biolabs, and 1 mM ATP in the buffer recommended by the manufacturer. After incubation overnight at 15C, the reaction is terminated by heating at 65C for 10 minutes. The reaction batch is diluted to about 100 ml in a buffer appropriate for the restriction endonuclease that cleaves the synthetic linker sequence. About 50 to 200 units of this endonuclease are added. The mixture is incubated for 2 to 6 hours at the appropriate temperature, then the fragment is subjected to agarose gel electrophoresis and purified as described above. The resulting fragment will then have ends with endings that were produced by cleaving with the restriction endonuclease. These are usually cohesive, so that the resulting fragment can then readily be linked to other fragments having the same cohesive ends. E. Removal of 5 '-terminal phosphates from DNA fragments During the plasmid cloning steps, treatment of the plasmid with phosphatase reduces the recircularisation of the vector (discussed on page 13 of d e Maniatis et al reference). After cleavage of the DNA with the correct restriction endonuclease, one unit of calf intestinal alkaline phosphatase obtained from Boehringer-Mannheim, Mannheim, is added. The DNA is incubated at 37C for one hour and then extracted twice with phenol and precipitated with ethanol. F. Linking of DNA fragments If fragments having complementary cohesive ends are to be linked to one another, about 100 ng of each fragment are incubated in a reaction mixture of 20 to 40 ml containing about 0.2 unit of T4 DNA ligase from New England Biolabs in the buffer recommended by the manufacturer. Incubation is carried out for 1 to 20 hours at 15C. If DNA fragments having blunt ends are to be linked, they are incubated as above except that the amount of T4 DNA ligase is increased to 2 to 4 units. G. Transformation of DNA into E. coli E. coli strain HB101 is used for most of the experiments. DNA is introduced into E. coli using the calcium chloride method, as described by Maniatis et al (1982), pages 250 and 251. H. Screening of E. coli for plasmids After transformation, the resulting colonies of E. coli are tested for the presence of the desired plasmid by means of a rapid plasmid isolation process. Two customary processes are described on pages 366 to 369 of the Maniatis et al (1982) reference. I. Large-scale isolation of plasmid DNA Processes for the isolation of plasmids from E. coli on a large scale are described on pages 88 to 94 of the Maniatis et al (1982) reference. J. Cloning in Ml 3 phage vectors In the following description it is to be understood that the double-stranded replicative form of the phage M13 derivatives is used for routine processes, such as cleaving with restriction endonuclease, linking etc.. Unless there is a specific indication to the contrary, enzymes can be obtained from Boehringer, Biolabs (BRL). They are used in accordance witii die manufacturer's instructions unless otiierwise indicated. K. Southern blot analysis The extracted DNA is first treated with restriction enzymes, then subjected to electro¬ phoresis in a 0.8 % to 1 % agarose gel, transferred to a nitrocellulose membrane [Southern E.M. (1975)] and hybridised with the DNA to be detected which has previously been subjected to nick-translation (DNA-specific activities of 5 x 10° to 10 x 10° c.p.m/mg). The filters are washed three times for 1 hour each time with an aqueous solution of 0.03M sodium citrate and 0.3M sodium chloride at 65C. The hybridised DNA is made visible by blackening an X-ray film over a period of 24 to 48 hours. EXAMPLE 1 Metabolism of T C1 GAs by C. maxima poly(A) "1" RNA in vitro translation products Endosperm and developing cotyledons of pumpkin (C. maxima) are rich sources of GA-biosynthetic enzymes. Poly(A) + RNA was isolated from immature cotyledons(lg) or endosperm (lOg) of C. maxima seed at 50 % maturity index using the 'Fast Track' mRNA isolation kit (Invitrogen). The yield of poly(A) + RNA from cotyledons (17.4 mg g fresh weight) was much higher than tiiat from endosperm (0.75 mg g fresh weight). In vitro translation of mRNA from cotyledons (1 mg), or endosperm (0.5 mg), was performed with rabbit reticulocyte lysates (Boehringer) using standard conditions, except that leucine and methionine were at 12.5 mM. As controls the reticulocyte lysate was in¬ cubated with tobacco mosaic virus RNA (1 mg), and cotyledon mRNA (1 mg) was in¬ cubated without lysate. After incubating for 2 h at 30°C the mixtures (50 ml) were supplemented with dioxygenase co-factors (4 mM 2- oxoglutarate, 0.5 mM FeSO4, 3 mM ascorbate and catalase (1 mg/ml)) and [ C] GA substrate (15,000 dpm; specific radio¬ activity 180 Ci/mol) added in 5 ml, and incubated for a further 3 h. Products were extracted and separated by reverse-phase high-performance liquid chromatography (HPLC) connected on-line to a radioactivity monitor. Figure 2A shows results from incubations of [^C] GA12 (a,b,c,d) with in vitro translation products using tobacco mosaic virus RNA (a), or mRNA from C. maxima cotyledons (c) or endosperm (d), or with cotyledon mRNA in the absence of the translation system (b). On the basis of HPLC retention times the peaks correspond to: GAj2 CD > G-A 5 (II). The products after translation of poly(A) + RNA from both tissues in rabbit reticulocyte lysates were shown to convert [ C] GA12 to [ C] GA15 (see Fig. 1) after incubation with the appropriate co-factors and analysis by HPLC (Fig. 2A). This 20-oxidase activity was higher in the translation products derived from the cotyledon mRNA. No activity was detected after incubation of the reticulocyte lysate with tobacco mosaic virus RNA or of the cotyledon mRNA without the translation system. EXAMPLE 2 Metabolism of I " Cl GAs by recombinant bacteriophage plaques An amplified cDNA library in λgtll derived from cotyledon poly(A) + RNA was immuno- screened with an antibody raised against a synthetic peptide (ValPheGlyGlySerAspGluSerLys) that had been produced on the basis of the amino acid sequence of a peptide resulting from trypsin digestion of purified GA12 20-oxidase from C. maxima endosperm [see SEQ ID NO 7]. An oligo(dT)-primed cDNA library was constructed in λgtll (Amersham) using cotyledon mRNA. The total library (70,000 clones) was amplified to give 3.6x10° plaque forming units (pfu)/ml of which 69 % were recombinant Immunoscreening of the amplified library was performed with 3,600 pfu on one 90 mm plate and probing with the 20-oxidase peptide antibody (1 mg/ml) and an alkaline phosphatase-conjugated anti-rabbit IgG second antibody. Seven positive plaques were obtained and these, as well as one negative plaque as control, were replated at 50 pfu/plate and rescreened. Nine positive plaques from one plate were assayed for GAj2 20-oxidase activity by incubating agar plugs (ca 5 ml) in Eppendorf tubes containing [~ ~ C] GA12 and co-factors as given in Example 1 in 25 ml SM buffer. Incubations were for 6 h, replenishing the co-factors every 2 h. Products were recovered after centrifugation (15,000 g for 2 min) and separated by reverse-phase HPLC connected on-line to a radioactivity monitor. All plaques were active giving up to 60 % conversion of substrate to [ C] GA15. Similarly, two positive plaques chosen from each of the remaining plates also expressed functional protein; in this case by taking larger (ca 25 ml) agar plugs the substrate was completely converted to mainly GA24/GA25. No positives were obtained after replating a negative plaque and rescreening with the antibody and two plaques from this plate chosen at random possessed no GA1220-oxidase activity. Figure 2B shows results from incubation of [ C] GA12 with plaques of single recom¬ binant λgtll bacteriophages that are not recognised (a) or recognised (b) by the anti GA12 20- oxidase antibody. On the basis of HPLC retention times and identification by gas chromatography - massspectrometry, the peaks correspond to: GA12 (I)» GA15 (II), GA24 and GA25 (V). Positive plaques, after purification, converted [ C] GA12 to radiolabelled GA15, GA24 and GA25 when agar plugs were incubated with die substrate and co-factors (Fig. 2B). Negative plaques contained no enzyme activity. The size of the inserts in the positive bacteriophages were shown using the polymerase chain reaction with λgtl 1 primers to be all about 1.4 kilobase pairs (kbp). EXAMPLE 3 Metabolism of r C1 GAs by recombinant 20-oxidase We examined the catalytic properties of die recombinant protein using a lysogen from a single bacteriophage. Recombinant GA 20-oxidase was prepared from a λgtl 1 lysogen in Y1089 essentially as in Sambrook, J., Fritsch, E.F. & Maniatis, T. Molecular Cloning: A Laboratory Manual 2nd edn (Cold Spring Harbor Laboratory Press, New York, 1989), but using a lysogen extraction buffer containing 200 mM Tris-HCl, pH 7.0 and 8 mM dithiothreitol. The activity of the protein was examined by incubating cell lysates with GA precursors. The capacity of the protein to oxidise [ C] GA12 was absolutely dependent on the addition of 2-oxoglutaric acid and was reduced by 73 and 90 %, respectively, when Fe^ + or ascorbic acid were omitted. The substrate specificity of the protein was also determined (Table 1). Different aliquots of the cell lysates were incubated with 100,000 dpm [ 14 C] GA12 (A) or [ 14 C] GA53 (B) and co-factors as described in Example 1 in a total volume of 250 ml for 4 h at 30°C, with fresh co-factors added after 2 h. In C, the substtates (200,000 dpm) were incubated with 250 ml of the lysate with co-factors for 6 h, replenishing the co- factors every 2 h. Products were extracted and analysed by HPLC-radiocounting and their identity con¬ firmed by combined gas chromatography-mass spectrometry (GC-MS). The specific radioactivities of products and substrates were the same. The results are shown in Table 1. Table 1 A. Incubations with [ C] GAj2 A Products(%) Supernatent (ml) GAj2 GAi5 GA 2 4/GA 2 5* 1.0 48 49 3 2.0 10 70 20 3.9 3 14 84 7.8 4 4 92** B. Incubations with [ 14 C] GA53 Products(%) Supernatant (ml) GA53 GA44 GA19 GA17 GA 2 0 *** 7.8 42 58 0 0 0 15.6 13 79 8 0 1 31.3 1 69 25 5 1 62.5 0 49 39 10 2 125 0 29 46 23 2 250 0 16 43 38 2 C. Incubations with 20-oxo-[ 1 C] GAs Subsu-ate Products(%) GA 24 GA 2 5/GA 9 (96)* GA 19 GAι 7 (49) GA 2 0(0.9) GA23 GA28(3.4)*** GAι(0.4) * Not resolved by HPLC. ** Shown by GC-MS to contain only [ 14 C] GA25 *** Identity of [* 4 C] GA was not confirmed by GC-MS. When the protein was incubated at increasing concentrations with r 4 C] GA12 (Table IA) sequential oxidation of the C-20 metiiyl group to the alcohol, aldehyde and carboxylic acid occurred to give, respectively, radiolabelled GA15, GA24 and GA25 as products. The corresponding 13-hydroxy GA products (GA44, GA19 and GA17) were also obtained, although at lower efficiency, when the lysate was incubated with [ 4 C] GA53 (Table IB). A comparison of the aldehyde substrates GA24 (non-hydroxylated), GA19 (monohydrox- ylated) and GA23 (dihydroxylated), showed that the efficiency of oxidation to the corres¬ ponding tricarboxylic acids decreased with increasing polarity of the substrate (Table 1C). In addition, the corresponding C19-GA products (GA9, GA20 and GAj), which are formed by loss of C-20 as CO2, were obtained in low yield. The results indicate that a single enzyme may catalyse each of the steps involving oxidation at C-20 during GA biosyndiesis, possibly also including die loss of C-20, although confirmation of this must await studies with the corresponding enzyme from a plant tissue in which C19-GA production forms a major pathway. EXAMPLE 4 Nucleotide sequence of GA 20-oxidase cDNA clone and derived amino acid sequence Restriction analysis of PCR-amplified bacteriophage inserts indicated the presence of an internal EcoRI site, but no internal BamHI sites. Bacteriophage DNA was prepared after infection of E. coli strain Y1090 (Amersham; 400 ml culture) and purified using a Lambda Phage Purification kit (Qiagen). After release of the insert with BamHI it was subcloned by insertion into the BamHI site of pUC18 and transformation of E. coli strain XLlblue. Plasmids were isolated from the transformants (Qiagen Plasmid Midi Kit) and one was sequenced on both strands by the dideoxynucleotide chain termination method. The selected clone has been deposited as pBll (E. coli) with die Agricultural Research Service Culture Collection (NRRL), Northern Regional Research Centre, 1815 North University Street, Peoria, π. 61604. The accession number is NRRL B-21096 and the deposition date is May 21, 1993. The nucleotide sequence of the selected clone and its derived amino acid sequence is shown in Figure 3. It contains an open reading frame of 1,158 nucleotides encoding a protein of Mr 43,321, which agrees closely with the value determined for the native enzyme. The sequence contains regions of homology with tiiose of previously cloned plant dioxygenases, including flavanone 3-hydroxylase, hyoscyamine 6-hydroxylase, E8, a ripening related gene of unknown function, and 1-aminocyclopropane-l-carboxylic acid oxidase, an enzyme involved in the production of the plant hormone ethylene. The conserved sequences include three histidine-containing motifs, two of which have been proposed as Fe-binding sites at the enzyme active centre. Amino acids that are conserved in other plant dioxygenases are shown in bold type. The sequence of the peptide against which the antibody for screening the expression library was raised is present close to the N-terminus and is underlined. It has one difference (P for V), which we found subsequendy to be due to an impurity in the tryptic peptide that was sequenced. Thus, all clones selected using this antibody would be near full-length and, as we have demonstrated, should encode functional proteins. Heterologous expression of the pumpkin GA 20-oxidase in E.coli. When the cDNA insert from pBll, encoding GA 20-oxidase from pumpkin, is expressed in E. coli, the protein produced catalyses the successive oxidation of the C-20 methyl group. Only 1% of the products are biologically active Ci9-gibberellins, formed by loss of C-20 as CO2; 99% of the products have a carboxylic acid group at C-20 and are not biologically active, nor can be converted to active gibberellins. Production of this enzyme in plants should, therefore, divert the C20 _ gibberellin intermediates of GA biosynthesis (mainly GA12 and GA53) to the carboxylic acid forms, so reducing the levels of active GAs. Example 5: Construction of a 35S-GA 20 chimaeric gene (the GA20 cDNA cloned into pCGN1761) GA20 oxidase is expressed in sense and antisense behind the constitutive 35S promoter. The cDNA encoding the GA20 oxidase gene is transferred to the vector pCGN1761 which carries the double 35S CaMV promoter and the tml transcriptional terminator on a pUC-derived plasmid. The construction of pCGN1761 is disclosed in example 23 on pages 39 to 41 of EP-A 0 392 225, which is incorporated herein by reference. The 1.4 BamHI fragment containing the GA20 oxidase gene is excised from the pUC-based plas¬ mid described in example 4 and ligated to an annealed molecular adaptor of the sequence 5'-AATTCGAACCCCTTCG-375'-GATCCGAAGGGGTTCG-3' (New England Biolabs #1105 and #1106), thus converting the BamHI ends to EcoRI ends. The ligation product is purified and cloned into the EcoRI site of pCGN1761 using standard techniques. Colonies carrying the cDNA in sense and antisense orientations relative to the double 35S promoter are recovered and are named pCGN1761-35S-GA20ox-A and pCGN1761-35S-GA20ox-B respectively. Example 6A: Transfer of the 35S-GA 20 fusion from pCGN1761-35S-GAox-A and pCGN1761-35S-GAox-B to the binary vector pCIB2001 The 35S-GA20 expression cassette is excised from constructions pCGN1761-35S-GAox-A and pCGN1761-35S-GAox-B described above by firstly cutting witii Hindiπ, rendering the linearized plasmid blunt by incubation with T4 DNA poly¬ merase, and then cutting with Hpal to release the 35S-GA20-tml insert. This is cloned into the StuI site of pCIB2001 generating binary vectors expressing the GA20ox gene in sense and antisense orientation behind the double 35 S promoter. Example 6B: Transfer of the 35S-GA 20 fusion from pCGN1761-35S-GAox-A and pCGN1761-35S-GAox-B to the direct gene transfer vector pCIB3064 The 35S-GA20 expression cassette is excised from constructions pCGN1761-35S-GAox-A and pCGN1761-35S-GAox-B described in example 5 by firstly cutting with HindlQ, rendering the linearized plasmid blunt by incubation with T4 DNA polymerase, and then cutting with Hpal to release the 35S-GA20-tml insert. This fragment is cloned into the Hindiπ site (rendered blunt by incubation with T4 DNA polymerase) of pCIB3064 [Koziel et al (1993)] generating vectors for direct gene transfer, utilizing PAT-gene selection, expressing the GA20ox gene in sense and antisense orientation behind the double 35S promoter. Example 7: Construction of a PR1-GA 20 chimaeric gene (the GA20 cDNA cloned into pCIB1004) The cDNA encoding the GA20 oxidase gene is transferred to the vector pCIB1004 to place it under the control of the chemically inducible PR la gene promoter. pCIB1004 is cleaved with Ncol and the 3' overhang is rendered blunt by incubation with T4 DNA polymerase. The construction of pCEB1004 is disclosed in example 21B on page 36 of EP-A 0 332 104, which is incorporated herein by reference. Subsequently BamHI non- phosphorylated linkers (New England Biolabs #1003) are ligated to the termini, and cleavage with BamHI releases an insert which is discarded. The 1.4A kb GA20-containing gene is excised from the construction of example 4 by cleavage with BamHI, and ligated to the BamHI site of the pCIB1004-derived fragment thus fusing the GA20 gene to the PRla promoter in both orientations. The resultant plasmids are termed pCIB1004-PRl-GA20ox-A (sense orientation and pCIB1004-PRl-GA20ox-B (antisense orientation). Example 8A: Transfer of the PR1-GA20 fusion from pCGN1004-PRl-GAox-A and pCGN1004-PRl-GAox-B to the binary vector pCIB2001 The PR-GA20 expression cassette is transferred from the pCIB1004-derived construct by partial digestion with Kpnl, recovery of a fragment of 5.6 kb in size, and ligation of this fragment into the Kpnl site of pCIB2001. This generates binary vectors carrying the GA20ox gene for expression behind the chemically regulated PRla promoter in sense and antisense orientations. Example 8B: Transfer of the PR1-GA20 fusion from pCGN1004-PRl-GAox-A and pCGN1004-PRl-GAox-B to the direct gene transfer vector pCIB3064 The PR-GA20 expression cassette is transferred from the pCIB1004-derived construct (example 7) by partial digestion with Kpnl, recovery of a fragment of 5.6 kb in size, incubation with T4 DNA polymerase to render termini blunt, and ligation of this fragment into the HindHI site (rendered blunt by incubation with T4 DNA polymerase) of pCIB3064 generating vectors for direct gene transfer, utilizing PAT-gene selection, expressing the GA20ox gene in sense and antisense orientation behind the chemically regulated PRla promoter. Example 9: Construction of a Pth-GA 20 chimaeric gene A pith-specific promoter from maize is used to express the GA20 gene in sense and antisense orientation in a tissue-specific manner. pCGN1761 is cleaved with Xhol and Sail and treated with T4 DNA polymerase to render termini blunt. The larger of the two resultant fragments is gel purified. A BamHI fragment carrying a pith-specific promoter is excised from the plasmid pCIB4433 (WO 93/07278) and ligated to the 1.4 kb fragment carrying the GA20-oxidase gene. Plasmid pCIB4433 has been deposited with the Agri¬ cultural Research Culture Collection (NRRL) (1818 N. University St., EL 61604) under the provisions of die Budapest Treaty under die Deposition No NRRL B-18999 on September 21, 1992. Following ligation, the mixture is treated with T4 DNA polymerase and the resultant blunt fragments are ligated into the pCGN1761-derived fragment. By restriction mapping and sequence analysis of the E. coli clones obtained it is possible to identify clones oriented with die Pth promoter driving expression of the sense GA20 gene upstream of the tml transcription terminator, and clones oriented with the Pth promoter driving expression of the GA20 gene in antisense orientation, upstream of the tml terminator. These clones are designated pCGN1761-Pth-GA20ox-A and pCGN1761-Pth-GA20ox-B respectively. Example 10A: Transfer of the pepC-GA20 fusion from pCGN1761-PepC-GAox-A and pCGN1761-PepC-GAox-B to the binary vector pCB2001 The Pth-GA20ox cassette is excised from pCGN1761-Pth-GA20ox-A and pCGN1761-Pth-GAox-B using Bgiπ and Hpal and cloned into the corresponding sites in pCIB2001. This generates binary vectors with GA20ox cloned in sense and antisense orientation under the regulation of the pith specific Pth promoter. Example 10B: Transfer of the PepC-GA20 fusion from pCGN1761-PeρC-GAox-A and pCGN1761-PepC-GAox-B to the direct gene transfer vector pCIB3064 The Pth-GA20ox cassette is excised from pCGN1761-Pth-GA20ox-A and pCGN1761-Pth-GAox-B by firstly cutting with Bgiπ, rendering the linearized plasmid blunt by treatment with T4 DNA polymerase, and tiien cutting with Hpal to release the Pth-GA20ox insert. This is cloned into the Hindiπ site (rendered blunt by incubation with T4 DNA polymerase) of pCIB3064 generating vectors for direct gene transfer, utilizing PAT-gene selection, expressing the GA20ox gene in sense and antisense orientation under the regulation of the pith specific Pth promoter. Example 11: Construction of the binary vector pCIB2001 TJS75 Kan is first created by digestion of pTJS75 [Schmidhauser et al, J Bacteriol 164: 446-455, 1985] with Narl to excise the tetracycline gene, followed by insertion of an AccI fragment from pUC4K [Messing et al, Gene 19: 259-268, 1982] carrying a Npt I gene. pCIB 200 is then made by ligating Xhol linkers to the EcoRV fragment of pCIB7 (con¬ taining the left and right T-DNA borders, a plant selectable nos/nptll chimaeric gene and the pUC polylinker, [Rothstein et al, Gene 53: 153-161, 1987] and cloning Xhol digested fragment into sail digested TJS75 Kan. pCIB2001 is made by cloning a new polylinker into the multiple cloning site of pCIB200 to give more unique restriction enzyme sites. PLANT TRANSFORMATION The recombinant DNA according to the invention comprising the GA20 oxidase encoding DNA sequence can be introduced into the plant cell using one of the well established Agrobacterium transformation systems or by means of direct gene delivery comprising, for example, microinjection [Crossway et al (1986); Neuhaus (1987)], electroporation [Riggs et al (1986)], direct gene transfer [Paszkowski et al, (1984)], or ballistic particle acceleration using, for example, devices available from Agracetus, Inc., Madison, Wisconsin and Dupont, Inc., Wilmington, Delaware. The detection of transformed plant cells may be accomplished using suitable selection systems well known in the art. A suitable selection marker gene may be present in the plant expression vector used in plant transformation or may alternatively be provided on one of the conventionally applied selection plasmids such as that described by Rothstein et al (1987) containing a selectable hygromycin resistance gene. The said plasmid may be introduced into the plant cell together with the recombinant DNA according to the invention comprising the GA20 oxidase encoding DNA sequence using co-transformation. Example 12: A. tumefaciens-mediated transformation of N. tabacum Explants roughly 5 to 10 mm are cut from young leaves 3 to 5 cm long and third to sixth from the apex of N. tabacum cv 'Xanthi nc' grown under axenic conditions [Facciotti and Pilet, 1979] in solid MS medium [Murashige and Skoog, 1962] containing 0.7 % phytagar (Gibco-BRL), 1 mg/1 I A A, 0.15 mg/1 kinetin. These explants are plated on solid MS medium containing 0.6 % phytagar, 40 mg/1 adenine sulfate, 2 mg/1 IAA, and 2 mg/1 kinetin on the surface of which is placed a #1 Whatman filter and incubated for 24 hr in the dark at 24C. Agrobacterium strains containing the binary vectors described above are grown overnight in LBMG at 30C on a shaker at 180 rpm. Explants are dipped into a bacterial suspension of 3.3 X 10° cells/ml for approximately 5 minutes, blotted on sterile paper towels, and re-plated on the same plates. After 48 hours explants are placed on selection medium containing the same plate medium as above plus 350 mg/1 cefotaxime and 100 mg/1 kanamycin. Co-cultivated control tissue is placed on the same medium but without kanamycin. The explants are transferred to fresh media every two weeks. Shoots are harvested 4 to 8 weeks after co-cultivation, placed on 50 ml culture tubes with 25 ml of solid MS medium containing 0.6 % phytogar, lmg/1 IBA, 350 mg/1 cefotaxime, and 100 mg/1 kanamycin. All tissue is grown at 24C to 28C, 12 hours of light, 12 hours dark, light intensity 6700 to 8400 lx. Shoots root in 1 to 2 weeks and are then transplanted to planting mix in 4" pots and placed in the "transgenic plant phytotron". Example 13: Leaf Disk Transformation of Tobacco Agrobacterium Strains containing the binary vectors described above are grown 18 to 24 hours in glutamate salts media adjusted to pH 5.6 and supplemented with 0.15 % mannitol, 50 mg/ml kanamycin, 50 mg/ml spectinomycin and 1 mg/ml streptomycin before they are diluted to an ODgQO of 0.2 in the same media without the antibiotics. The bacteria are then grown for three to five hours before dilution to an ODgoo °f 0.2 to 0.4 for inoculation of discs of 5 to 7 mm punched from leaves of N. tabacum cv xanthi that have been grown aseptically in GA7 containers, following a modification of the methods ofHorsch et α/ (1985). The leaf disks are maintained on 0.7 % agar containing Murashige and Skoogs major and minor salts (MS), 1 mg/1 benzyladenine and 1 mg/ml ΝAA for two days before transfer to the same media containing 50 mg/ml kanamycin, 100 mg/ml carbenicillin and 100 mg ml mefoxin. Shoots which form on the disks are excised and propagated until six plantiets are obtained by subculturing die shoot tips on MS media containing 50 mg/ml kanamycin in GA7 containers. The plandets are rooted on medium containing no hormones and 50 mg/ml kanamycin, transferred to soil and hardened in a phytotron before transfer to the greenhouse for induction treatment with chemical regulators. At flowering time flowers are induced to selfpollinate. Seeds are harvested following maturation. Example 14: Production of Transgenic Tobacco Callus and Plants Agrobacterium strains containing the binary vectors described above are used to transform callus forming from leaf disks. Callus forming on kanamycin-containing MSBΝ selection medium is maintained on a callus growth medium comprised of MS major, minor salts and Fe-EDTA (Gibco #500-1117; 4.3 g/1), MS vitamins, 100 mg/1 myo-inositol, 20 g/1 sucrose, 2 mg/1 NAA and 0.3 mg/1 kinetin. The callus can be used to regenerate transgenic plants by transferring callus pieces to MSBN medium and following methods described. Example 15: Transformation of Carrot Agrobacterium strains containing the binary vectors described above are grown as described in Example 13. The bacteria, diluted to an OD Q TJO of 0.2 to 0.4, are then used for inoculation of discs cut from surface sterilized carrots. To surface sterilize the carrots they are peeled and then soaked 20 minutes in a 10 % solution of chlorox. The carrots are rinsed with sterile water, sliced into 5 mm pieces and placed basal side up onto water agar. 20 to 50 ml of bacteria are then applied to the upper surface of the disks. After 7 days the disks are transferred to 0.7 % agar containing MS salts, 3 % sucrose, 0.1 mg/12,4-D, 50 mg/ml kanamycin, 100 mg/ml carbenicillin, and 100 mg/ml mefoxin. Callus forming around the cambial ring is excised and placed on 0.7% MS agar supplemented with 3 % sucrose 0.1 mgA 2,4-D, 50 mg ml kanamycin, 100 mg/ml carbenicillin, and 100 mg ml mefoxin. After the callus has been grown it is cut into small pieces and randomized onto four plates of the same media. Example 16: Transformation of Sunflower Agrobacterium strains containing the binary vectors described above are grown as described. The bacteria, diluted to an ODgoo of 0.2 to 0.4, are then used for inoculation of stems of sunflower plants prepared as follows: Sunflower seeds are soaked 10 mins in 10 % captan followed by 10 mins in 10 % chlorox and rinsing with sterile water. The seed coats are removed and the seeds are germinated on 0.7 % water agar in the dark for three days, after which they are placed into a labline incubator set at 23 C with a 12 hour day and night. The seedlings are grown for one week before decapitation and inoculation of the bacteria onto the cut stem surface. After one week the inoculated stems are cut and placed on 0.7 % agar containing MS salts, 3 % sucrose, 2 mg/ml NAA, 1 mg/ml BAP, 100 mg/ml carbenicillin, 100 mg/ml mefoxin and 50 mg/ml kanamycin. The callus is transferred to fresh media every two weeks until sufficient quantity is obtained for 4 plates. Half of the callus growing from the virulent Agrobacterium strains is transferred to media without hormones containing 50 mg/ml kanamycin. Example 17: Transformation of Tomato Agrobacterium strains containing the binary vectors described above are grown as described in Example 13. The bacteria, diluted to an ODβOO of 0.2 to 0.4, are then used for inoculation of stems of tomato seedlings prepared as follows: Tomato seeds are soaked 20 mins in 10 % chlorox and rinsed with sterile water. The seeds are germinated on 0.7 % water agar in the dark for three days, after which they are placed into a labline incubator set at 23C with a 12 hour day and night. The seedlings are grown for one week before decapitation and inoculation of the bacteria onto the cut stem surface. After one week, the inoculated stems are cut and placed on 0.7 % agar containing MS salts, 3 % sucrose, 2 mg/ml NAA, 1 mg/ml BAP, 100 mg/ml carbenicillin, 100 mg ml mefoxin and 50 mg/ml kanamycin. The callus is transferred to fresh media every two weeks until sufficient quantity is obtained for 4 plates. Example 18: Transformation of Cotton Agrobacterium strains containing the binary vectors described above are grown as described. The bacteria, diluted to an ODgoo of 0.2 to 0.4, are then used for inoculation of cotton cotyledons prepared as follows: The cotton seeds are soaked 20 mins in 10 % chlorox and rinsed with sterile water. The seeds are germinated on 0.7 % water agar in the dark. The seedlings are grown for one week before inoculation of the bacteria onto the cotyledon surface. The inoculated cotyledons are allowed to form a callus before they are cut and placed on 0.7 % agar containing MS salts, 3 % sucrose, 100 mg/ml carbenicillin, and 100 mg/ml mefoxin. The callus is transferred to fresh media every three weeks until sufficient quantity is obtained for 4 plates. Half of the callus growing from the virulent Agrobacterium strains is transferred to media without hormones containing 50mg ml kanamycin. Example 19: Preparation of a Special Type of Callus of Zea mays, Elite Inbred line Funk 2717 ZeaAmays plants of the inbred line Funk 2717 are grown to flowering in the greenhouse, and self pollinated. Immature ears containing embryos approximately 2 to 2.5 mm in length are removed from the plants and sterilized in 10 % chlorox solution for 20 minutes. Embryos are aseptically removed from the kernels and plated with d e embryo axis downwards on OMS medium containing 0.1 mg/1 2,4-D, 6 % sucrose and 25 mM L-proline solidified with 0.24 % (initiation medium). After two weeks' culture in the dark at 27C, the callus developing on the scutellum is removed from the embryo and plated on B5 medium (Gamborg et al, 1968) containing 0.5 mg/1 2,4-D and solidified with 0.24 % Gelrite . The callus is subcultured every two weeks to fresh medium. After a total of eight weeks after placing the embryos on the initiation medium, the special type of callus is identified by its characteristic morphology. This callus is subcultured further on the same medium. After a further period of two months, the callus is transferred to , and serially subcultured on N6 medium containing 2 mg/12,4-D and solidified with Example 20: Preparation of a Suspension Culture of Zea mays, Elite Inbred Funk 2717 The callus described above is subcultured for a total of a least six months. The type of callus chosen for subculture is relatively non-mucilaginous, granular and very friable, such that it separates into small individual cell aggregates upon placing into liquid medium. Cultures containing aggregates with large, expanded cells are not retained. Approximately 500 mg aliquots of the special callus of Zea mays elite inbred funk 2717 are placed into 30 ml of N6 medium containing 2 mgΛ 2,4-D in 125 ml Delong flasks. After one week of culture at 26C in the dark on a gyratory shaker (130 rpm, 2.5 cm throw), the medium is replaced with fresh medium. The suspensions are again subcultured in this way after another week. At that time, the cultures are inspected, and those which do not show large numbers of expanded cells are retained. Suspension cultures containing aggregates with large, expanded cells are discarded. The preferred tissue consists of densely cytoplasmic dividing cell aggregates which have a characteristically smoother surface that the usual type of cell aggregates. The cultures retained have at least 50 % of the cells represented in these small aggregates. This is the desired morphology. These suspensions also have a rapid growth rate, with a doubling time of less than one week. The suspension cultures are subcultured weekly by transferring 0.5 ml PCV into 25 ml of fresh medium. After four to six weeks of subculture in this fashion, the cultures increase two- to three-fold per weekly subculture. Cultures in which more than 75 % of the cells are of the desired morphology are retained for further subculture. The lines are maintained by always choosing for subculture the flash whose contents exhibit the best morphology. Periodic filtration through 630 mm pore size stainless steel sieves every two weeks is used in some cases to increase the dispersion of the cultures, but is not necessary. Example 21: Preparation of Protoplasts from Suspension Cultures of Zea mays 1 to 1.5 ml PCV of the suspension culture cells from above are incubated in 10 to 15 ml of a filter-sterilized mixture consisting of 4 % cellulase RS with 1 % Rhozyme in KMC (8.65 g 1 KC1, 16.47 g/1 MgCl2.6H2O and 12.5 g/1 CaCl2.2H2θ, pH 5.6) salt solution. Digestion is carried out at 30C on a slow rocking table for a period of 3 to 4 hours. The preparation is monitored under an inverted microscope for protoplast release. The protoplasts which are released are collected as follows: The preparation is filtered through a 100 mm mesh sieve, followed by a 50 mm mesh sieve. The protoplasts are washed through the sieves with a volume of KMC salt solution equal to die original volume of enzyme solution. 10 ml of the protoplast preparation is placed in each of several disposable plastic centrifuge tubes, and 1.5 to 2 ml of 0.6 M sucrose solution (buffered to pH 5.6 witii 0.1 % MES and KOH) layered underneath. The tube is centrifuged at 60 to 100 x g for 10 minutes, and the protoplasts banding at the interface collected using a pipette and placed in a fresh tube. The protoplast preparation is resuspended in 10 ml of fresh KMC salt solution, and centrifuged for five minutes at 60 to 100 x g. The supernatant is removed and discarded, and the protoplasts resuspended gently in die drop remaining, and then 10 ml of a 13/14 strength KMC solution gradually added. After centrifuging again for five minutes, the supernatant is again removed and the protoplasts resuspended in a 6/7 strength KMC solution. An aliquot is taken for counting, and the protoplasts again sedimented by centrifugation. The protoplasts are resuspended at 10' per ml in KM-8p medium or in 0.5 M mannitol containing 6 mM MgCl2 or other suitable medium for use in transformation as described in the following examples. This protoplast suspension is used for transformation and is cultured as described below. Example 22: Transformation of Zea mays Protoplasts by Electroporation A. All steps except the heat shock are carried out at room temperature (22 to 28C). The protoplasts are resuspended in the last step of above in 0.5 M mannitol containing 0.1 % MES and 6 mM MgCl2- The resistance of this suspension is measured in the chamber of a Dialog Electroporator and adjusted to 1 to 1.2 kL using a 300 mM MgCl2 solution. The protoplasts are heat-shocked by immersing the tube containing the sample in a water bath at 45C for five minutes, followed by cooling to room temperature on ice, 4 mg of linearized plasmid and 20 mg of calf thymus carrier DNA are added to aliquots of 0.25 ml of this suspension. 0.125 ml of a 24 % PEG solution (MW8000) in 0.5 M mannitol containing 30 mM MgCl2 are added to the protoplasts. The mixture is mixed well but gently, and incubated for 10 minutes. The sample is transferred to the chamber of the electroporator and samples pulsed three times at 10 second intervals, at initial voltages of 1500, 1800, 2300 or 2800 Vcm "1 , and an exponential decay time of 10 msec. The protoplasts are cultured as follows. The samples are plated in 6 cm petri dishes at room temperature. After a further 5 to 15 minutes, 3 ml of KM-8p medium containing 1.2 % SeaPlaque agarose and 1 mg/1 2,4-D are added. The agarose and protoplasts are mixed well and the medium allowed to gel. B. This is repeated with one or more of the following modifications: The resistance of the protoplast preparation is adjusted to 0.5 to 0.7 kL . THe PEG used is PEG with a MW of 4000. No PEG is added, or one-half volume of 12 % PEG is added. The pulses are applied at intervals of three seconds. The protoplasts are plated after the electroporation in dishes placed on a plate cooled to a temperature of 16C. The protoplasts are placed in tubes after the electroporation step, washed with 10 ml ø f 6/7 strength KMC solution or with W5 solution (comprised of 380 mg/1 KC1, 18.375 g/1 CaCl2-2H2θ, 9 g/1 NaCl; 9Ag/l glucose, pH 6.0), then collected by centrifugation at 60 x g for 10 minutes, resuspended in 0.3 ml of KM medium and plated as in A. The calf thymus carrier DNA is not added. Example 23: Transformation of Zea mays Protoplasts by Treatment with PEG A. The protoplasts are resuspended at the last step of above in a 0.5 M mannitol solution containing 12 to 30 mM MgCl2- A heat shock of 45°C for five minutes is given as described. The protoplasts are distributed in aliquots for transformation in centrifuge tubes, 0.3 ml of suspended protoplasts per tube. During the next 10 minutes the following are added: DNA and PEG solution (MW 6000, 40 % containing 0.1 M Ca(NO3)2 and 0.4 M mannitol; pH 8 to 9 with KOH) to give a final concenttation of 20 % PEG. The aliquots are incubated for 30 minutes with occasional gentle shaking, and then the protoplasts are placed in petri dishes (0.3 ml original protoplast suspension per 6 cm diameter dish) and cultured as described. B. This is repeated and the protoplasts are washed after 30 minutes of incubation in the PEG solution of above, by adding 0.3 ml of W5 solution five times at two- to three-minute intervals. The protoplast suspension is centrifuged, the supernatant removed, and the protoplasts are cultured as described. C. The above is repeated with the modification that the final concentration of PEG is between 13 and 25 %. Example 24: Regeneration of Callus From Protoplasts The plates containing the protoplasts in agarose are placed in the dark at 26°C. After 14 days, colonies arise from the protoplasts. The agarose containing the colonies is transferred to the surface of a 9 cm diameter petri dish containing 30 ml of N6 medium containing 2 mg/1 2,4-D, solidified with 0.24 % Gelrite. This medium is referred to as 2N6. The callus is cultured further in the dark at 26°C and callus pieces subcultured every two weeks onto fresh solid 2N6 medium. Example 25: Selection of Transformed Callus of Zea mays The above example is repeated with the modification that an appropriate selection agent is added to the 2N6 medium in order to select for transformed cells. Example 26: Regeneration of Corn Plants A. Callus is placed on 2N6 medium for maintenance and on ON6 (comprising N6 medium lacking 2,4-D) and N61 medium (comprising N6 medium containing 0.25 mg/1 2,4-D and 10 mg/1 kinetin) to initiate regeneration. Callus growing on ON6 and N61 media is grown in the light (16 hours/day Ught of 840 to 8400 lx from white fluorescent lamps). Callus growing on N61 medium is transferred to ON6 medium after two weeks, as prolonged time on N61 medium is detrimental. The caUus is subcultured every two weeks even if the caUus is to be transferred again on the same medium formulation. Plantlets appear in about four to eight weeks. Once the plantlets are at least 2 cm tall, they are transferred to ON6 medium in GA7 containers. Roots form in two to four weeks, and when the roots look weU-formed enough to support growth, the plantlets are transferred to soil in peat pots, under a Ught shading for the first four to seven days. It is often helpful to invert a clear plastic cup over the transplants for two to three days to assist hardening off. Once the plants are estabUshed, they are treated as normal com plants and grown to maturity in the greenhouse. In order to obtain progeny plants are self pollinated or crossed with wild type. B. The above example is repeated with the modification that an appropriate selection agent is added to the medium used to maintain the callus. Example 27: Production of transgenic maize plants Tissue Immature maize embryos, approximately 1.5-2.5 mm in length, are excised from an ear of genotype 6N615 14-15 days after poltination. The mother plant is grown in the greenhouse. Before excision, the ear is surface sterilized with 20 % Clorox for 20 minutes and rinsed 3 times with sterile water. Individual embryos are plated scutellum side in a 2 cm square area, 36 embryos to a plate, on the callus initiation medium, 2DG4 + 5 chloramben medium (N6 major salts, B5 minor salts, MS iron, 2 % sucrose, with 5 mg/1 chloramben, 20 mgΛ glucose, and 10 ml G4 additions Table 1) added after autoclaving. TABLE 1 - G4 Additions Ingredient per Uter medium Casein hydrolysate 0.5 g Proline 1.38 g Nicotinic acid 0.2 mg Pyridoxine-HCl 0.2 mg Thiamine-HCl 0.5 mg ChoUne-HCl 0.1 mg Riboflavin 0.05 mg Biotin 0.1 mg Folic acid 0.05 mg Ca pantothenate 0.1 mg p-aminobenzoic acid 0.05 mg B120.136 g Bombardment Tissue is bombarded using the PDS-lOOOHe BioUstics device. The tissue is placed on the shelf 8 cm below the stopping screen shelf. The tissue is shot one time with the DNA/gold micTocarrier solution, 101 dried onto the macrocarrier. The stopping screen used is hand punched using 10x10 stainless steel mesh screen. Rupture discs of 1550 psi value are used. After bombardment, the embryos are cultured in the dark at 25C. Preparation of DNA for delivery The microcarrier is prepared essentially according to the instructions suppUed with the BioUstic device. Callus formation Embryos are transferred to callus initiation medium with 3 mgΛ PPT 1 day after bombardment. Embryos are scored for caUus initiation at 2 and 3 weeks after bombardment. Any responses are transferred to callus maintenance medium, 2DG4 + 0.5 2,4-D medium supplemented with an appropriate selection agent dependent on the selection marker gene used. Callus maintenance medium is N6 major salts, B5 minor salts, MS iron, 2 % sucrose, with 0.5 mgΛ 2,4-D, 20 mgΛ glucose, and 10 ml G4 additions added after autoclaving. Embryogenic callus is subcultured every 2 weeks to fresh maintenance medium containing an appropriate selection agent. All callus is incubated in the dark at 25 C. The Type I callus formation response is 18 %. Every embryo which produced callus is cultured as an individual event giving rise to an individual line. Regeneration After 12 weeks on selection, the tissue us removed from callus maintenance medium with an appropriate selection agent and is placed on regeneration medium and incubated at 25 C using a 16 hour Ught (50 E. m-2, s-l)/8 hour dark photoperiod. Regeneration medium is 0.25MS3S5BA (0.25 mgΛ 2,4-D, 5 mgΛ BAP, MS salts, 3 % sucrose) for 2 weeks followed by subculture to MS3S medium for regeneration of plants. After 4 to 10 weeks, plants are removed and put into GA 7's. Example 28: Preparation of Embryogenic Suspensions from Tissue of DactyUs glomerata L. (Orcha-rdgrass) A. Embryogenic caUus is initiated from basal sections of the youngest leaves of greenhouse-grown orchardgrass plants (Dactylis glomerata L.) as described by Hanning and Conger (1982). The leaves are surface sterilized by immersion in a 1:10 dilution of Chlorox solution (5.25 % sodium hypochlorite; The Clorox Company, Oakland, Ca.) for about 10 minutes and then cut aseptically into small segments of 1 to 5 mm in length or in diameter. These segments are plated on sterile SH-30 medium containing 0.8 % agarose as a geUing agent CaUus and/or embryogenic structures appear within 2 to 6 weeks after plating, upon culture at about 25°C. Embryogenic caUus is maintained by subculturing onto fresh SH-30 medium every 2 to 4 weeks and culturing in the dark at 25°C. B. Embryogenic suspension cultures are initiated by placing approximately 0.5 g fresh weight of embryogenic caUus into 50 ml of Uquid medium described by Gray and Conger (1985) containing 45 mM dicamba and 4 g/titer casein hydrolysate. The suspension cultures are grown at 27°C under a 16 hours Ught (3300 lx), 8 hours dark photoperiod on a gyratory shaker at about 130 rpm in 125ml Delong flasks sealed with a metal cap and parafilm. After approximately four weeks the large clumps are aUowed to settle for about 30 seconds and 10 ml aUquots of the supernatant medium containing small ceU clusters are removed and transferred to 50 ml of fresh medium. This process is repeated every 3 to 4 weeks using the most successful cultures as judged by smaUer clump size and better quality based on the presence of small, cytoplasmic ceUs. After 5 to 8 transfers the suspensions are essentially free of non embryogenic cells and the majority of the embryogenic cell clusters are quite small (150 to 2000 mm). Example 29: Isolation and Purification of Dactylis glomerata L. Protoplasts Protoplasts are prepared from embryogenic suspension cultures of above by aseptically filtering the cells on a Nalgene 0.2 mm filter unit and then adding 0.5 g fresh weight cells to each 12.5 ml of protoplasts enzyme mixture in a petri dish. The enzyme mixture consists of 2 % CeUulase RS, 7 mM CaCl2xH2θ, 0.7mM NaH2PO4xH2O, 3mM MES (pH 5.6), glucose (550mOs/kg H2O of pH 5.6), and is filter sterilized. The mixture is swirled on an orbital shaker at about 50 rpm in dim (< 420 lx) light for about 4 to 5 hours. The digest is then sieved through a stainless steel sieve (100 mm mesh size) and distributed into 12 ml centrifuge tubes which are centrifuged at about 60 to 100 x g for about 5 minutes. The protoplast-containing sediment is then washed three times with protoplast culture medium KM-8p adjusted to 550 mOs/kg H2O with glucose. At this point a flotation step may be included for further purification of the protoplasts. In this case, the washed protoplasts are layered atop 10 ml of KM-8p culture medium adjusted to 700 mOs/kg H2O with sucrose. After centrifugation at 60 to 100 x g for about 10 minutes, protoplasts banding at the interface are collected using a fine pipette. Finally, die protoplasts are resuspended in 1 to 2 ml KM-8p culture medium and sieved dirough a stainless steel screen (20 mm mesh size). The protoplasts released are collected and washed and resuspended in KM-8p medium for culture or in osmotically adjusted medium suitable for transformation according to the examples below. Example 30: Dactylis glomerata L. Protoplast Culture and Growth of CaUus A. The purified protoplasts are plated at a density of about 5x lCr protoplasts per ml in KM-8p culture medium containing 1.3 % SeaPlaque agarose (FMC Corp., Marine CoUoids Division, Rockland, Maine, USA) and 30 to 40 % of conditioned medium (obtained from 3 to 4 week-old Dactylis glomerata L. embryogenic suspension cultures by filtering the medium through a sterile Nalgene 0.2 mm filter, making the medium 550 mOs/kg H2O by addition of glucose, and again filter sterilizing). The plates are then placed in the dark at a constant temperature of 28°C. After 10 to 14 days the agarose is cut into wedges and placed into 'bead culture' as described by ShiUito et al. (1983) using 20 ml SH-45 suspension culture medium with 3 % sucrose per 3 ml original agarose embedded culture. The plants are put on a platform shaker and agitated at about 50 rpm in light at 670 lx. New suspension cultures are formed as the colonies grow out of the agarose and release cells into the liquid medium. The resultant suspension cultured cells are plated onto agar-solidified SH-30 medium and placed in the dark at 25°C until callus is formed. B. Protoplasts are cultured as described above except that die culture media contains no conditioned medium. Example 31: Transformation of Dactylis glomerata L. Protoplasts by Means of Electroporation A. Immediately after purification of the protoplasts, electroporation is performed according to ShiUito et al. (1985) using linearized plasmid. The protoplasts are resuspended after the last wash at a density of about 7 x 10" protoplasts per ml in the electroporation buffer (0.4 M mannitol, 6 mM MgCl2). The protoplasts are placed in 0.7 ml atiquots in 10 ml plastic centrifuge tubes. Plasmid DNA and sonicated calf thymus DNA (Sigma) to give final concentrations of 10 mg/ml and 50 mg/ml respectively is added to the tubes. Then 0.38 ml PEG solution [24 % PEG 6000 in 0.4 M mannitol, 30 mM MgCl2, 0.1 % MES (pH 5.6)] is added and the solution gently mixed. The protoplast suspension is transferred into the chamber of a Dialog Electroporator and 10 pulses of 3250 Vcm ' l initial voltage and exponential decay constant of 10 msec applied at 30 sec intervals. The sample is removed from the chamber, and placed in a 10 cm diameter petri dish. 10 ml of KM-8p medium containing 1.2 % SeaPlaque agarose is added, the protoplasts distributed evenly throughout the medium, and the agarose allowed to gel. B. The above is repeated except that the initial voltage used is 3500 Vcm -1 , 4000 Vcm "1 , 5000 Vcm "1 , 3000 Vcm "1 , or 2500 Vcm '1 . Example 32: Transformation of Dactylis glomerata L. Protoplasts by Treatment with PEG A. PEG mediated direct gene transfer is performed according to Negrutiu, I. et al., (1987). The DNA used is linearized plasmid described. The protoplasts are suspended foUowing the last wash in 0.5 M mannitol containing 15 mM MgCl2 at a density of about 2 x 10° per ml. The protoplast suspension is distributed as 1 ml aliquots into 10 ml plastic centrifuge tubes. The DNA is added as described above, and then 0.5 ml of the PEG solution added (40 % PEG 4000 in 0.4 M mannitol, 0.1 M Ca(NO3)2, pH 7.0). The solutions are mixed gentiy and incubated for 30 minutes at room temperature (about 24°C) for 30 minutes with occasional shaking. 1.4 ml of the wash solution is then added, and tiie contents of the tube gentiy mixed. The wash solution consists of 87 mM mannitol, 115mM CaCl2, 27mM MgCl2, 39mM KC1, 7mM Tris-HCl and 1.7 gΛ myo-inositol, pH 9.0. Four further 1.4ml aUquots of wash solution are added at 4 minute intervals, with mixing after each addition. The tube is then centrifuged at about 60 x g for about 10 minutes, and the supernatant discarded. The sedimented protoplasts are taken up in 1 ml KM-8p culture medium, and placed in a 10 cm petri dish. 10 ml of KM-8p medium containing 1.2 % SeaPlaque agarose is added. The protoplasts are evenly distributed throughout die medium and the agarose allowed to gel. B. This is repeated with one or more of the foUowing modifications: (1) The pH of the wash solution is adjusted to 5.6 or 7.0. (2) The PEG used is PEG of MW 6000, PEG of MW 2000 or PEG of MW 8000. (3) The wash medium consists of 154 mM NaCl, 125 mM CaCl2, 5 mM KC1, 5 mM glucose, pH to 6.0 with KOH, of 0.2 M CaCl2, 0.1 % MES, pH 6.0 with KOH, or of 0.2 M CaCl2, 7 mM Tris/HCl, pH 9.0 with KOH. Example 33: Transformation of Dactylis glomerata L. Protoplasts by Electroporation or PEG Treatment Transformation is carried out as described above except that the protoplasts are treated at 45°C for about 5 minutes prior to distribution of the aUquots into tubes for transformation or after distribution of the aliquots, and before addition of the PEG. Example 34: Selection of Transformed Colonies A. The culture plates (petri dishes) containing the protoplasts are incubated for 10 days in the dark at about 25°C and then cut into 5 equal slices for 'bead cultures' (ShiUito et al., 1983). Four of the slices are placed each into 20 ml SH-45 culture medium containing 4 gΛ casein hydrolysate and an appropriate selection agent dependent n the selection marker gene used in plant transformation. The fifth slice is put into 20 ml of the same medium but without selection agent as a non-selected control. After 4 to 5 weeks the putative transformed proptoplast-derived cell colonies growing in the presence of the selection marker are cut out of the agarose and placed into a 19 mm petri dish with 2 ml of liquid SH-45 medium containing an appropriate selection agent which is agitated at about 50 rpm on a orbital shaker. After another 4 to 5 weeks aU colonies which grow to make new suspensions are transferred into 125 ml Erlenmeyer flasks and grown in a manner similar to the parent suspension culture, except that an appropriate selection agent is included in the medium. The new suspensions are subcultured every 1 to 3 weeks using SH-45 medium containing 4 gΛ casein hydrolysate and an appropriate selection agent. Cells from these suspensions are also plated on solidified SH-30 medium containing an appropriate selection agent and incubated at about 25°C in the dark. CalU grown from the plated ceUs are subcultured every two weeks onto fresh medium. The cells which grow in the presence of the selection marker are presumed to be transformants. B. Section is carried out as described except that the protoplast-derived cell colonies growing in the presence of the selection marker containing medium are placed on agar plates of SH-30 medium containing the selection marker and incubated at about 25°C in the dark. Example 35: Regeneration of Transformed Dactylis glomerata L. Plants A. Dactylis glomerata L. callus (obtained as described) derived from protoplasts is grown on solidified SH-30 medium, and subcultured every two weeks. Any embryos which form are removed and plated on germination medium (SH-O) and placed in the light (3800 to 4600 lx). Germination of these embryos occurs in 1 to 4 weeks and the resultant plantlets are placed on SH-O medium in die light to form root systems. They are moved into the greenhouse at tiie six to twelve leaf stage, and hardened off gradually. B. Callus (obtained as described) derived from protoplasts is grown on SH-O medium solidified with 0.24 % Gelrite in the light (3800 to 4600 lx), and subcultured every two weeks. The resultant plantlets are placed on a 1:1 mixture of SH-O and OMS media soUdified with a combination of 0.12 % Gelrite and 0.4 % agar in the light to form root sy stems. They are moved to the greenhouse at the six to twelve leaf stage, and hardened off gradually. C. Small plantlets are obtained as described in Examples 35A and 35B, and are placed on OMS medium solidified with 0.8 % agar in the Ught to form root systems. They are moved to the greenhouse at the six to twelve leaf stage, and hardened off gradually. D. Small plantlets are obtained as described in Example 35A above and are placed on a 1:1 mixture of SH-O and OMS media soUdified with a combination of 0.12 % GelRite and 0.4 % agar in the Ught to form root systems. They are moved to the greenhouse at the six to twelve leaf stage, and hardened off gradually. Example 36: Production of transgenic wheat plants Cell Culture Maintenance CaUus cultures are maintained on IMS medium as described for example by "Murashige, T. and Skoog F., 1962, Physiol. Plant 15, 473 - 497" (MS salts, vitamins, iron, 3 % sucrose, 0.7 % agar, 1 mg Uter 2,4-D). The suitable caUus cultures comprise among others Type H caUus (a friable and embryogenic type of caUus) obtained from "shoot-competent" ceU cultures as described in "W. Wang and H. Nguyen, 1990, Plant Cell Reports 8 639-642") after recurrent subculture and visual selection. They are subcultured every two weeks and are kept in the dark at 26°C. Suspension cultures are maintained in IMS Uquid medium and are subcultured twice weekly. They are kept in the dark at 26°C and shaken at "125 rpm. Cell Preparation for Bombardment The cells are given a plasmolysis treatment before bombardment. Packed cell volume is measured and cells are diluted in IMS liquid medium with added osmoticum: 0.4M sorbitol for suspension cells and 0.6M sorbitol for callus cells. Cells are diluted such that the final packed ceU volume per target is 1/20 ml for a fine suspension and 1/10 ml for caUus. Diluted cells are placed in a 250 ml flask containing a stir bar and are stirred for a minimum of 30 minutes, up to a few hours. To plate the ceUs, 2 ml is withdrawn from the flask and pipetted into the top of a vacuum flask onto which a Whatman 2.5 cm GFA filter has been placed. The vacuum is applied until the cells are dried onto the filter, the filters are placed on 60 x 15 mm petri plates containing 5 ml of solid post bombardment plasmolysis medium: IMS containing 0.2M sorbitol for suspension cells, or 0.4M sorbitol for callus ceUs. Two filters are plated on each dish. Particle Preparation Gold particles (1.0 micron; from Bio-Rad) are washed by aliquoting into a microfuge tube, adding "1 ml 100 % ethanol, vortexing, spinning down, removing the supernatant, and repeating twice with sterile water. After the final wash, as much water is removed as possible and polylysine solution (0.02 % polylysine + 15mM ammonium acetate) is added to completely immerse the particles. The particles are vortexed, spun, and the supernatant removed. The particles are allowed to dry overnight in a laminar flow hood or for 30 minutes under a gentle nitrogen stream. For a "full" particle preparation, weigh out 10 mg particles and place in sterile microfuge tube containing a stir bar. Add 100 ml (lmg ml)DNA (according to step I), vortex, add 10 ml 100 mM Na2HPO4, vortex, add 10 ml 100 mM CaCl2, vortex, add 380 ml 100 % ethanol, vortex. Stir suspension vigorously on stir plate while pipetting 3 ml onto each plastic flier (projectile). Allow particles to dry onto fliers for at least 15 minutes before bombarding. Bombarding CeU Cultures Bombarding of ceU cultures is carried out using a device as described in EP-A .... Invert the petri plate containing the ceU filters onto the platform on top of the stage, centered over the particle flight opening. Place the clear Ud over the top of the platform. Place a microprojectile onto the breech pin and close the breech. Push the "arm" button to fiU the reservoir with the appropriate amount of helium gas (usually 1800 - 1900psi). PuU the vacuum on the chamber to " 27 mm. Turn off the vacuum, and push the "arm" and "fire buttons. Move the "arm" button on die "off position. Each filter is usuaUy shot twice. Post bombardment Culture and Section After bombardment the cells are kept in the dark overnight The next day, filters are removed from plasmolysis medium and placed on IMS medium. Selection is applied 7 - 10 days post-bombardment for suspension ceUs and after 14 days for callus ceUs. Cells are scraped off the filters and spread onto the surface of plates containing IMS plus an appropriate selection agent, dependent on the selection marker gene used in plant transformation. Plates are incubated in the dark for several weeks. Resistant colonies that arise after a few weeks are transferred to IMS + selection agent. Coloni that continue to proliferate for about 3 - 4 weeks are then transferred to "0.5MS" maintenance medium: MS salts, vitamins, iron, 3 % sucrose, 0.7 % agar, 0.5 mgΛiter 2,4-D. Tissue is subcultured onto this medium biweekly until embryogenic structures or tissue seems suitable for regeneration. Regeneration Tissue is transferred to MS medium containing either 3 mg/Uter BAP or 1 mgΛiter NAA + 5 mgΛiter GA, and plates are moved to the light. After 2 - 4 weeks, tissue is transferred to MS medium without hormones. Shoots that appear are placed in Magenta boxes containing either MS medium without hormones or MS medium with 0.5 mgΛiter NAA. When sufficient root and shoot growth has occurred, plantlets are transferred to soil and placed in a phytotron. Example 37: GA 20-oxidase DNA from Arabidopsis thaliana. (a) Isolation of genomic DNA from Arabidopsis thaliana. Seeds of Arabidopsis thaliana Landsberg erecta are surface steriUsed by treatment with 5% sodium hypochlorite solution in 0.01% Tween-20 (Sigma), washed twice with water and suspended in 0.15% agar. The seeds are sown onto 0.8% agar containing Murashige and Skoog Medium supplemented with B5 vitamins (Sigma) and 5% sucrose in sterile Magenta containers (Sigma). Plants are grown for 4 weeks at 20°C and shoot material is frozen in Uquid nitrogen and stored at -70°C. Genomic DNA is isolated essentially as described by Murray and Thompson (Murray MG and Thompson WF (1980)). The frozen tissue, lOg, is ground to a slurry in an ice-cooled mortar with a smaU amount of acid-washed sand. The homogenate is transferred to a polypropylene centrifuge tube and an equal volume of 2% (w/v) CTAB (cetyltrimethylammonium bromide, Sigma), 1.4M NaCl, 0.1M Tris-Cl pH8.0, 20mM EDTA added . After gentle mixing, the tube is incubated at 67°C for 20min with occasional mixing. The tube is removed from the water bath and 0.5 volumes of chloroform added, mixed gentiy and left at room temperature (20°C) for 20 min with occasional inversion. The tube is centrifuged at 2000g for 5 min at room temperature, the upper phase removed to a new tube and tiie lower phase discarded. To the upper phase is added 0.1 vol of 10% (w/v) CTAB, 0.7M NaCl and the chloroform extraction above is repeated. The upper phase is again decanted to a new tube and 2 volumes of 1% (w/v) CTAB, 50mM Tris-Cl, pH8.0, lOmM EDTA added. This is mixed gentiy and left at room temperature for 1 hour, then centrifuged at 5000g for 5 min. The pellet is dissolved in 50% (w/w) CsCl in TE buffer with etiiidium bromide at 0.5 mg/ml. The solution is transferred to a Quick-seal tube (Beckman) and centrifuged in a vertical rotor (Beckman VTi90) for 16 hours at 80,000 rpm at 20°C. The DNA is visualised under natural Ught and removed with the aid of a syringe and needle. Ethidium bromide is removed by extraction four times with 5 volumes of butan-1-ol, previously equiUbrated against NaCl-saturated water. The solution is diluted by the addition of 3 volumes of TE buffer (lOmM Tris-Cl pH8.0, ImM EDTA) and DNA precipitated with 2 volumes of EtOH. The DNA is pelleted by centrifugation at 10,000g for 10 min at 0°C, washed with 70% EtOH, dried in vacuo, and dissolved in TE buffer. The DNA concentration is determined by its absorbance at 260nm. (b) Construction of a cDNA library. Seeds of Arabidopsis thaliana gal are induced to germinate by overnight incubation in a lOmM solution of GA3, shaking at room temperature. The seeds are washed twice with water, suspended in 0.15% agar in water and sown directly onto seed compost. Plants are grown for 5 weeks and shoot tissue harvested directly into Uquid nitrogen and stored at -70°C. Poly A + RNA is isolated as described by Bartels and Thompson (1983). Double stranded cDNA is produced from 5mg mRNA using an oUgo-dT primer with the cDNA Synthesis Plus Kit (Amersham) and EcoRI adapters added using the λgtl 1 Cloning Kit (Amersham). The cDNA is tigated into EcoRI-cut, dephosphorylated λZapE arms (Stratagene) and packaged using Gigapack Gold (Strategene). A primary Ubrary of 320,000 recombinants is produced, and half of this is amplified by passage through E coli XL 1 -Blue (Stratagene) as described by the manufacturer. (c) Plating the cDNA library for screening. A 50 ml aliquot of 2xYT (1.6% Bactotryptone, 1% yeast extract, 0.5% NaCl) including 0.2% maltose and lOmM MgSO4 is inoculated with a single colony of E coli XL 1 -Blue. This is grown overnight at 30 C, transferred to a sterile centrifuge tube and spun down at 2000 x g for 5 min, room temperature. The cells are resuspended in lOmM MgSO4. In sterile 15ml tubes, 500ml E. coli cells is mixed with 50,000 recombinant bacteriophage from the amplified Ubrary and incubated at at room temperature for 10 min followed by 37 C for 15 min. Molten top agarose (0.75% in 2xYT/ 0.2% maltose/lOmM MgSO4), 6.5 ml, is added at 48 C and the tube contents quickly poured onto a prewarmed 10cm x 10cm plate of 1.5% agar in 2xYT/ 0.2% maltose/lOmM MgSθ4. The plates are incubated inverted at 37 C for 6 hours and then stored overnight at 4°C. Duplicate nitrocellulose filters are labelled and placed onto the agar plates for 1 min each. The filters are air dried and treated for 5 min each in 1.5M NaCl, 0.5M NaOH (denaturation); 3M NaCl, 1M Tris-Cl pH 6.5 (neutralization); 0.6M NaCl, 60mM trisodium citrate (fixation). The filters are again air dried on filter paper and baked in vacuo, between layers of filter paper, at 80 C for 2hrs. (d) Preparation of labelled probe. The insert from clone pAt2204, consisting of a PCR fragment from Arabidopsis genomic DNA, is labelled with P^ * ^ by primer extension. Plasmid DNA, 2mg in 20mg TE buffer, is denatured by the addition of 5ml of 1M NaOH, incubated at room temperature for 5 min and neutraUzed by spin-desalting through a 0.5ml column of Sepharose CI^6B in TE, spun at 2,000 rpm for 2.5 min. To 10ml of this denatured DNA is added 2ml universal sequencing primer (New England Biolabs) and 2ml lOOmM Tris-Cl pH8.0, 50mM MgCl2- This is incubated at 37°C for 15 min and 4ml 32 P-dCTP (lOmCi/ml; 3,000Ci/mmol; Amersham), 1ml dGAT mix (0.2mM each dGTP, dATP, dTTP), 1ml Klenow DNA polymerase (lu/ml; Gibco-BRL) are added. After 15min at room temperature (20°C), 1ml of 2mM dCTP is added; after a further 5 min at room temperature, 2.2ml of lOx Hindiπ buffer (Gibco-BRL) and 10 units of HinάTfl are added and the tube incubated at 37°C for 45 min. To terminate the reaction, 8ml of formamide dye loading mix (Pharmacia) is added and the DNA is denatured by heating to 95°C for 2 min. The products are loaded onto a 1.5cm well on a 1mm thick, 20cm x 20cm polyacrylamide gel (6% (w/v) polyacrylamide (acrylamide:methylenebisacrylamide = 39:1), 1 x TBE (90mM Tris, 90mM Boric acid, 2.5mM EDTA), 8M urea). The gel is run at 25W constant power for 1 hour, and one glass plate is removed and the gel covered with cling-film. The position of the labelled band is identified by autoradiography against Kodak X-OMAT LS for 5min. The labelled band is excised from the gel and placed into a dialysis bag, 1 cm wide, with 0.4ml TE buffer. This is sealed at each end with a dialysis clip and placed in a horizontal electrophoresis tank filled with TBE buffer. The labelled DNA is eluted at lOOv for 30 min and recovered from the dialysis bag in the TE buffer. (e) Hybridization. Nitrocellulose filter Ufts prepared as above are wetted in water and prehybridized for 2 hours at 42°C in hybridization buffer (50% formamide, 50mM NaPi pH 6.3, 0.75M NaCl, 75mM trisodium citrate, 0.1% (w/v) bovine serum albumin, 0.1% (w/v) Ficoll 400, 0.1% (w/v) polyvinylpyrroUdone, 0.1% (w/v) sodium dodecyl sulphate (SDS), lOOmg/ml sonicated calf thymus DNA). The probe is boiled for 2 min, mixed with 25 ml of hybridization buffer and sealed into a polythene bag with the prehybridized filters. Hybridization is carried out at 42°C overnight, and unbound probe is removed by washing in 0.3M NaCl, 30mM trisodium citrate, 0.1% (w/v) SDS at room temperature for 15 min, and in 15mM NaCl, 1.5mM trisodium citrate, 0.1% SDS at 60°C for 10 min. Positively-hybridizing plaques are identified by autoradiography against Kodak X-OMAT AR film with intensifying screens, overnight at -70°C. Positive plaques are isolated in pure form by plating the primary positives and probing lifts with the labelled insert of pAt2204 as described above. Pure recombinant λZapH clones are rescued into pBluescript (Stratagene) as described by the manufacturer. (f) DNA sequencing. The DNA sequence of the inserts of the primary cloned PCR fragments are obtained with the T4 Polymerase Sequencing Kit (Pharmacia). The insert of the fuU-length clone pAt2301 is sequenced by the construction of a nested set of transposon insertion clones, usng the TNI 000 Nested Set Kit (Gold Biotechnology, St. Louis, Mo.) foUowed by sequencing of individual clones with the T4 Polymerase Sequencing Kit (Pharmacia). Example 38: Isolation and characterisation of DNA clone pAt2301 and pAt2353, encoding a gibbereUin 20-oxidase from Arabidopsis thaliana. (a) PCR ampUfication and cloning of internal fragments of 20-oxidase-related genes from Arabidopsis genomic DNA. Degenerate, oUgodeoxynucleotide primers are designed based on amino acid regions conserved between the Cucurbita maxima cotyledon gibberellin 20-oxidase and other plant dioxygenases, including the tomato E8 ripening-related protein, tomato ethylene-froming enzyme, hyoscamine 6-hydroxylase from Hyoscyamus niger, barley flavanone 3-hydroxylase and the A2 gene from maize. The upstream and downstream primers contained restriction endonuclease cleavage sites for Hindπi and EcoRI, respectively, at their 5' termini. Upstream primer Amino acid: Asn Tyr Tyr Pro Thr Cys DNA: 5 ' - GCAAGCTT-A A(CT)-TA(TC)-TA(TC)-CCX- ACX-TG- 3 ' Downstream primer Amino acid: Phe Val He Asn Ue Gly Asp DNA: 3' -AA(GA)-CAX-TA(AGT)-TT(GA)-TA(AGT)-CCX-CT-TAAGCG- 5' PCR reactions contained 50ng genomic DNA from Arabidopsis thaliana strain Landsberg erecta (Redei, GP (1962)), 2.5μg each degenerate primer, 25μM each dNTP and 1 unit of AmpliTaq (Perkin Elmer Cetus) in a total volume of 25μl AmpliTaq buffer containing 1.5mM MgCl 2 , and overlayed with 25μl mineral oU. Reactions are incubated at 94°C for 5 mins followed by 40 cycles of 94°C 1 min, 35°C 2 min, 72°C 3 min. The 72°C step is increased by 5 sec each cycle. The reactions are then incubated at 72°C for 10 minutes. The products of PCR ampUfication are separated by electrophoresis through a 1.5% agarose gel in Tris-Borate-EDTA buffer (90mM Tris, 90mM Boric acid, 2.5mM EDTA). A faint band of approx 190 bp is identified and eluted from the gel into lOOμl of TE buffer (lOmM Tris-Cl pH8.0, ImM EDTA), lμl of which is used as substrate in a PCR reaction under the conditions described above. The products are again separated by agarose gel electrophoresis and the 190 bp ampUfied band purified from the agarose. This is digested with EcoRI and Hind-H and one thenth of the products ligated to 100 ng of pUC19 (Pharmacia), previously digested with EcoRI and HindHI and dephosphorylated. The products of die ligation reaction are introduced into E. coli strain XL 1 -Blue (Statagene) by transformation and grown on 2xYT agar plates containing 100μg/ml ampicilUn. Plasmid DNA is isolated from single colonies, and sequenced by the dideoxynucleotide chain termination mediod. One of these clones, pAt2204, contained an insert whose predicted amino acid sequence is 67% identical to that of pumpkin gibberellin 20-oxidase: AATTACTACCCTACGTGTATAAAACCAGATCTCACACTAGGAACAGGACCTCATTGTGAT AsnTyrTyrProThrCysIleLysProAspLeuThrLeuGlyThrGlyProHisCysAsp CCAACATCTCTTACCATCCTTCACCAAGACCATGTTAATGGCCTTCAAGTCTTTGTGGAA ProThrSerLeuThrlleLeuHisGlnAspHisValAsnGlyLeuGlnValPheValGlu AATCAATGGCGCTCCATTCGTCCCAACCCCAAGGCCTTTGTAATTAACATCGGA AsnGlnTrpArgSerlleArgProAsnProLysAlaPheVallleAsnlleGly (b) Isolation of a full-length cDNA clone corresponding to PCR clone pAt2204. The insert of pAt2204 is labelled with 32 p-dCTP and used to probe nitrocellulose filter lifts of a full-length cDNA library, constructed in λZapII (Stratagene) from poly-A 4 RNA isolated from shoot material of the gibbereUin-deficient gal mutant of Arabidopsis thaliana (Koornneef M and van der Veen J H (1980)). The hybridisation is carried out in 50% fromamide, 50mM sodium phosphate pH 6.3, 0.75M NaCl, 75mM sodium citrate, 0.1% bovine serum albumin, 0.1% Ficoll 400, 0.1% polyvinylpyrrolidone 360, 0.1% sodium dodecyl sulphate and lOOμg/ml salmon testes DNA at 42°C overnight. FUters are washed in 15mM NaCl, 1.5mM sodium citrate at 42°C for lOmin. Hybridising plaques are identified by autoradiography and purified by successive rounds of hybridisation. Positive clones are converted into pBluescript clones by plasmid rescue and characterised by EcoRI digestion and DNA sequencing. Clone pAt2353 and clone pAt2301, containing a 1.3 kbp insert, are chosen for heterologous expression studies. (c) Expression of cDNA clone pAt2301 in E. coli The 1.3kbp insert of pAt2301 is excised with EcoRI. purified by agarose gel electrophoresis and Ugated to expression vector pTrcHisA (Invitrogen), previously cut with EcoRI and dephosphorylated. Ligation products are introduced into E. coli strain TOP 10 (Invitrogen) by transformation and selected by growth on 2xYT agar witii ampicUUn at lOOμg/ml. Plasmid DNA is isolated from a number of the resulting clones and the orientation of the cDNA insert determined by HindHI digestion. Clone pAt2328 contained a cDNA insert in sense orientation, and is used to inoculate 50ml of 2xYT containing carbeniciUin at lOOμg/ml. After 2 hrs growth shaking at 37°C, IPTG (Isopropyl-b-D-thiogalactopyranoside) is added to ImM and the cultures are grown for a further 5 hrs. The cells are collected by centrifugation and suspended in 4ml of lOOmM Tris-Cl pH7.5, 4mM DTT and sonicated on ice for a total of 90 sees. The samples are then frozen in liquid nitrogen, thawed by hand and insoluble material removed by centrifugation at 15,000 x q f or 5 min. The resulting supernatant material is stored at -80°C and subsequendy used for enzyme assay. The supernatant (90 μl) is incubated witii [ 14 C]GA 12 (10,000 dpm) and dioxygenase co-factors as given in Example 1 in lOOμl total volume at 30°C for 5 hr. Separation of products by HPLC showed production of [ 14 C]GA 15 , the identity of which is confirmed by combined gas chromatography-mass spectrometry (GC-MS). Example 39: Isolation of cDNA clone YAP169, encoding a gibberellin 20-oxidase from Arabidopsis thaliana. A TBLASTN program is ran on the DBEST (database of expressed sequence tags) held at the NIH (BLAST@NCBI.NLM.NIH.GOV) using the full amino acid sequence of the Arbabidopsis cDNA clone At2301 to search for related sequences. The search program translates the DNA sequences in the database into amino acid sequences in both orientations and all three reading frames. The DBEST database contains partial sequences for cDNAs obtained at random as part of the systematic Arbabidopsis cDNA sequencing program. The method for producing Arbabidopsis sequences has been published by Hδfte et αZ (1993). Running the TBLASTIN program an additional clone (YAP 169) can be identified that owing to its sequence homology to clone pAt2301 is likely to encode a dioxygenase. Expressing the cDNA in E coli as described previously confirms that the expressed protein has 20-oxidase activity. Clone YAP169 was kindly provided by M Delseny of the University of Perpignan, France. Example 40: Transformation of Arabidopsis thaliana (a) Construction of a PR 1 -tml vector. Construction of a vector in which die double CaMV 35S promoter in pCGN1761 is replaced by d e chemically-inducible promoter from die Arabidopsis PRla gene. The oligonucleotide 5'-GAGAATTCTAAGTTGATAATGGTTATTG-3' is used in conjunction with the M13 universal sequencing primer in a PCR reaction, using plasmid pATPRl-P as substrate. The product of this reaction, a 4.2 kbp fragment containing the PR1 promoter, is digested with EcoRI and Hindiπ. Plasmid pCGN1761 is digested with EcoRI and Hindlll to remove the double 35 S promoter and the resulting 5 kbp vector fragment is Ugated with the PR1 promoter fragment. The ligation products are introduced into E. coli by transformation and a colony containing the PR1 promoter identified. This plasmid is named pPRl-tml. (b) Construction of 35S-20-oxidase (Arabidopsis )chimaeric genes (the three Arabidopsis 20-oxidase cDNAs each cloned into pCGN1761) The three GA 20-oxidase cDNAs (At2301, At2353 and YAP169) are each expressed in sense and antisense orientation behind the constitutive CaMV 35S promoter, by PCR amplification of each open reading frame and transfer into the vector pCGN1761. An oligonucleotide is synthesized corresponding to the translation initiation codon and the succeeding 12-13 bases of the coding strand of each cDNA, and incorporating an EcoRI site at the 5' ends: for pAT2301 the oligonucleotide is 5'-GAGAATTCAAAATGGCC- GTAAGTTTCG-3'; for pAt2353 the oligonucleotide is 5'-GAGAATTCAGAAATGG- CGATACTATGC-3'; for YAP169 the oligonucleotide is 5'-GAGAATTCAAAA- ATGGCAACGGAATGC-3'. Each of these oligonucleotides is used in conjunction with the M 13 universal sequencing primer in PCR reactions, using the appropriate plasmid substrate (pAt2301, pAT2353 and YAP169 respectively). The PCR products from each reaction are digested with EcoRI and cloned into the EcoRI site of pCGN1761 using standard techniques. Colonies carrying each of the three cDNA inserts in sense and antisense orientations relative to the 35S promoter are recovered and are named pCGN1761-35S-At2301-sense, pCGN1761-35S-At2301-antisense, pCGN1761-35S- At2353-sense, pCGN1761-35S-At2353-antisense, pCGN1761-35S-YAP169-sense and pCGN1761-35S-YAP169-antisense respectively. (c) Construction of PRl-20-oxidase (Arabidopsis) chimaeric genes (the three Arabidopsis 20-oxidase cDNAs each cloned int pPRl-tml. The EcoRI-digested PCR products derived from pAt2301, pAt2353 and YAP169, described above, are cloned into the EcoRI site of pPRl-tml, to yield each Arabidopsis GA 20-oxidase cDNA in sense and antisense orientation with respect to the chemically-inducible PR1 promoter. The constructs are named pPRl-At2301 -sense, pPRl-At2301 -antisense, pPRl-At2353-sense, pPRl-At2353-antisense, pPRl- YAP169-sense and pPRl-YAP169-antisense. (d) Transfer of the 35S-20-oxidase (Arabidopsis) fusions from pCGN1761-35S- At2301-sense. pCGN1761-35S-At2301-antisense. pCGN1761-35S-At2353-sense. pCGN1761-35S-At2353-antisense, pCGN1761-35S-YAP169-sense and pCGN1761-35S- YAP169-antisense to the binary vector pCIB200. The 35S-20-oxidase expression cassettes are excised from constructs pCGN1761-35S- At2301-sense, pCGN1761-35S-At2301-antisense, pCGN1761-35S-At2353-sense, pCGN1761-35S-At2353-antisense, pCGN1761-35S-YAP169-sense and pCGN1761- 35S-YAP169-antisense by digestion or partial digestion with Xbal. Each of these cassettes is cloned into the Xbal site of pCIB200 [see Example 11] generating binary vectors capable of expressing the cDNA inserts of pAt2301, pAt2353 and YAP 169 in sense and antisense orientation behind the double 35S promoter. (e) Transfer of the PRl-20-oxidase (Arabidopsis) fusions from pPR 1 - At2301 -sense, pPRl-At2301-antisense. pPRl-At2353-sense, pPRl-At2353-antisense. pPRl-YAP169- sense and pPRl-YAP169-antisense to the binary vector pCIB200. The PRl-20-oxidase expression cassettes are excised from constructs pPRl- At2301-sense, pPRl-At2301 -antisense, pPRl-At2353-sense, pPRl-At2353-antisense, pPRl-YAP169-sense and pPRl-YAP169-antisense by digestion or partial digestion with Xbal. Each of these cassettes is cloned into the Xbal site of pCIB200 generating binary vectors capable of expressing the cDNA inserts of pAt2301, pAt2353 and YAP169 in sense and antisense orientation behind the chemically-inducible PR1 promoter. (f) Transformation of Arabidopsis thaliana. The above constructs wiU be introduced into Arabidopsis thaliana by Agrobacterium tumifaciens-mediated transformation as described in Example 12 and 13. 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Genet. 22: 421-477 (1988) Patent Literature EP-A0267159 WO89/07647 EP-A0306139 US-P4,^45,050 EP-A0332104 EP-A0434616 EP-A0462065 EP-A0478502 SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: (A) NAME: Long Ashton Research Station (B) STREET: None (C) CITY: Long Ashton, Bristol (E) COUNTRY: UK (F) POSTAL CODE (ZIP) : BS18 9AF (G) TELEPHONE: (0275) 392181 (H) TELEFAX: (0275) 394007 (ii) TITLE OF INVENTION: Regulation of Plant Growth (iii) NUMBER OF SEQUENCES: 17 (iv) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC coπpatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: PatentIn Release #1.0, Version #1.25 (EPO) (v) CURRENT APPLICATION DATA: APPLICATION NUMBER: GB 9311147.4 (2) INFORMATION FOR SEQ ID NO: 1: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 1395 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA to mRNA (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: Cucurbita maxima (vii) IMMEDIATE SOURCE: (B) CLONE: Clone pBll (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1: CTTCTTTGCA TGCAATGGCT TTGAACGGCA AGGTGGCAAC CGAATCCGCT CCCTCAAACT 60 TGAATGAGGA GATGAAAGGG GAGTACCGTC CGCCATTTGG GGGCTCCGAC GAGTCAAAGG 120 TGCCGGAGGA TTTCATTTGG TCGGAAAAGT TTGAGGCATC CGAGTTGCTG CCGGTGCTGG 180 ATGTTCCAAC TATTGACTTG GAAAAGTTTA TGAGTGGCGA CAAAAGTTAT GTGGAAGAGG 240 CGACAAGGCT GGTGGATGAG GCTTGTAGAC AACATGGCAT ATTTTTTGTG GTGAACCATG 300 GAGTGGACAT AGAAATGATG GGCCGTGTTC ATGACTGTAT GAATGAGTTC TTTACAATGC 360 CTTTGGATGT GAAGCAGAGG GCTAAGAGGA AGGTAGGTGA GAGTTATGGA TATACCAATA 420 GCTTCTTTGG GAGATTCGCG TCCAATCTTC CATGGAAGGA AACCTTTTCC CTTCGCTGTG 480 TGGCTGCTCA AAACTCCTCC GCGGCTCATG ACTATGTTCT TGACACTTTA GGCCCATCAT 540 TCTCCCATCA TGGGAAGGCG TATCAAGAGT GTGGGATAGC ATTGAACGAG CTTGGTACGA 600 AGATTGTGGA GCTTTTGGGG CTTAGCCTTG GCATTTCAAG AGAATACTTC AAGAATTTCT 660 TCGAGGACAA CGATTCAATA TTGAGGCTTA ATTACTACCC AACATGCGAC AAGCCAGAGG 720 TTGTGTTGGG AACTGGCCCT CACACTGATC CCACCTCCGT CACAATCCTT CACCAAGACC 780 CTGTCAGTGG CCTTCAAGTG TGCTCCAATG ATCAATGGTA TTCAATTCCT CCAAACCCAG 840 AAGCCTTTGT CATCAACATC GGTGACACTT TCACGTCTCT CACGAATGGG ATTTACAAGG 900 GCTGCATACA CCGCGCTGTA GTGAATTCCA TGAATGCAAG AAAATCATTG GCCTTCTTTC 960 TGTGTCCATC GCATGACAAA GTGGTGAGAG CACCGGAGGA ATTGGTGGAG AAGAGTCCAC 1020 CACGAAAGTA TCCAGATTAT AAATGGCCAA TGTTGCTTGA AATGACCCAA AAGCGTTACC 1080 GACCTGATTG CAACACTTTG GAAGCCTTCA AAACTTGGGT TCAAGAGGGA AAGGCGTTGG 1140 ACACTGGGTC CACTATTACC GCCCCGTCTG CTTAAACCAA CCGTATCTAT GTCTCTCTAT 1200 GTATGCCAAT AAGTGTTTCT ACATTTACGA GCTTTCTAGG GAAGAAGAAC ATCGTGTAGG 1260 GTTCGGTCTA TGTCTGTCTT ATGTGTTGCT GGAAGTTGCA ATTAAAATAA ACCCTTTAAT 1320 ATCACATGTT CTTACTTTGC TCAAAAAAAA AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA 1380 AAAAAAAAAA AAAAA 1395 (2) INFORMATION FOR SEQ ID NO: 2: ' (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 386 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (v) FRAGMENT TYPE: internal (vi) ORIGINAL SOURCE: (A) ORGANISM: Cucurbita maxima (vii) IMMEDIATE SOURCE: (B) CLONE: Protein zu clone pBll (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 2: Met Ala Leu Asn Gly Lys Val Ala Thr Glu Ser Ala Pro Ser Asn Leu 1 5 10 15 Asn Glu Glu Met Lys Gly Glu Tyr Arg Pro Pro Phe Gly Gly Ser Asp 20 25 30 Glu Ser Lys Val Pro Glu Asp Phe He Trp Ser Glu Lys Phe Glu Ala 35 40 45 Ser Glu Leu Leu Pro Val Leu Asp Val Pro Thr He Asp Leu Glu Lys 50 55 60 Phe Met Ser Gly Asp Lys Ser Tyr Val Glu Glu Ala Thr Arg Leu Val 65 70 75 80 Asp Glu Ala Cys Arg Gin His Gly He Phe Phe Val Val Asn His Gly 85 90 95 Val Asp He Glu Met Met Gly Arg Val His Asp Cys Met Asn Glu Phe 100 105 110 Phe Thr Met Pro Leu Asp Val Lys Gin Arg Ala Lys Arg Lys Val Gly 115 120 125 Glu Ser Tyr Gly Tyr Thr Asn Ser Phe Phe Gly Arg Phe Ala Ser Asn 130 135 140 Leu Pro Trp Lys Glu Thr Phe Ser Leu Arg Cys Val Ala Ala Gin Asn 145 150 155 160 Ser Ser Ala Ala His Asp Tyr Val Leu Asp Thr Leu Gly Pro Ser Phe 165 170 175 Ser His His Gly Lys Ala Tyr Gin Glu Cys Gly He Ala Leu Asn Glu 180 185 190 Leu Gly Thr Lys He Val Glu Leu Leu Gly Leu Ser Leu Gly He Ser 195 200 205 Arg Glu Tyr Phe Lys Asn Phe Phe Glu Asp Asn Asp Ser He Leu Arg 210 215 220 Leu Asn Tyr Tyr Pro Thr Cys Asp Lys Pro Glu Val Val Leu Gly Thr 225 230 235 240 Gly Pro His Thr Asp Pro Thr Ser Val Thr He Leu His Gin Asp Pro 245 250 255 Val Ser Gly Leu Gin Val Cys Ser Asn Asp Gin Trp Tyr Ser He Pro 260 265 270 Pro Asn Pro Glu Ala Phe Val He Asn He Gly Asp Thr Phe Thr Ser 275 280 285 Leu Thr Asn Gly He Tyr Lys Gly Cys He His Arg Ala Val Val Asn 290 295 300 Ser Met Asn Ala Arg Lys Ser Leu Ala Phe Phe Leu Cys Pro Ser His 305 310 315 320 Asp Lys Val Val Arg Ala Pro Glu Glu Leu Val Glu Lys Ser Pro Pro 325 330 335 Arg Lys Tyr Pro Asp Tyr Lys Trp Pro Met Leu Leu Glu Met Thr Gin 340 345 350 Lys Arg Tyr Arg Pro Asp Cys Asn Thr Leu Glu Ala Phe Lys Thr Trp 355 360 365 Val Gin Glu Gly Lys Ala Leu Asp Thr Gly Ser Thr He Thr Ala Pro 370 375 380 Ser Ala 385 (2) INFORMATION FOR SEQ ID NO: 3: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 1259 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA to mRNA (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: Arabidopsis thaliana (vii) IMMEDIATE SOURCE: (B) CLONE: pAt2301 (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 3: AATCTCTCAA AATGGCCGTA AGTTTCGTAA CAACATCTCC TGAGGAAGAA GACAAACCGA 60 AGCTAGGCCT TGGAAATATT CAAACTCCGT TAATCTTCAA CCCTTCAATG CTTAACCTTC 120 AAGCCAATAT CCCAAACCAA TTCATCTGGC CTGACGACGA AAAACCTTCC ATCAACGTTC 180 TCGAGCTTGA TGTTCCTCTC ATCGACCTTC AAAACCTTCT CTCTGATCCA TCCTCCACTT 240 TAGATGCTTC GAGACTGATC TCTGAGGCCT GTAAGAAGCA CGGTTTCTTC CTCGTGGTCA 300 ATCACGGCAT CAGCGAGGAG CTTATATCAG ACGCTCATGA ATACACGAGC CGCTTCTTTG 360 ATATGCCTCT CTCCGAAAAA CAGAGGGTTC TTAGAAAATC CGGTGAGAGT GTTGGCTACG 420 CAAGCAGTTT CACCGGACGC TTCTCCACCA AGCTTCCATG GAAGGAGACC CTTTCTTTCC 480 GGTTTTGCGA cGACATGAGC CGCTCAAAAT CCGTTCAAGA TTACTTCTGC GATGCGTTGG 540 GACATGGGTT TCAGCCATTT GGGAAGGTGT ATCAAGAGTA TTGTGAAGCA ATGAGTTCTC 600 TATCATTGAA GATCATGGAG CTTCTCGGGC TAAGTTTAGG CGTAAAACGG GACTACTTTA 660 GAGAGTTTTT CGAAGAAAAC GATTCAATAA TGAGACTGAA TTACTACCCT CCATGTATAA 720 AACCAGATCT CACACTAGGA ACAGGACCTC ATTGTGATCC AACATCTCTT ACCATCCTTC 780 ACCAAGACCA TGTTAATGGC CTTCAAGTCT TTGTGGAAAA TCAATGGCGC TCCATTCGTC 840 CCAACCCCAA GGCCTTTGTG GTCAATATCG GCGATACTTT CATGGCTCTA TCGAACGATA 900 GATACAAGAG CTGCTTGCAC CGGGCGGTGG TGAACAGCAA GAGCGAGAGG AAGTCACTTG 960 CATTCTTCTT GTGTCCGAAA AAAGACAGAG TAGTGACGCC ACCGAGAGAG CTTTTGGACA 1020 GCATCACATC AAGAAGATAC CCTGACTTCA CATGGTCTAT GTTCCTTGAG TTCACTCAGA 1080 AACATTATAG AGCAGACATG AACACTCTCC AAGCCTTTTC AGATTGGCTC ACCAAACCCA 1140 TCTAAGAAAT AAAATATTCA TGTCTTGTCT TGTTAGTTAC TAGTATCTTC TTTATATTTC 1200 ATGTATGTAT ATGGTAATAG GCAATAACAC CTTTTAGCAT CTCAAAAAAA AAAAAAAAA 1259 (2) INFORMATION FOR SEQ ID NO: 4: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 377 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: Arabidopsis thaliana (vii) IMMEDIATE SOURCE: (B) CLONE: zu Clone pAT2301 (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 4: Met Ala Val Ser Phe Val Thr Thr Ser Pro Glu Glu Glu Asp Lys Pro 1 5 10 15 Lys Leu Gly Leu Gly Asn He Gin Thr Pro Leu He Phe Asn Pro Ser 20 25 30 Met Leu Asn Leu Gin Ala Asn He Pro Asn Gin Phe He Trp Pro Asp 35 40 45 Asp Glu Lys Pro Ser He Asn Val Leu Glu Leu Asp Val Pro Leu He 50 55 60 Asp Leu Gin Asn Leu Leu Ser Asp Pro Ser Ser Thr Leu Asp Ala Ser 65 70 75 80 Arg Leu He Ser Glu Ala Cys Lys Lys His Gly Phe Phe Leu Val Val 85 90 95 Asn His Gly He Ser Glu Glu Leu He Ser Asp Ala His Glu Tyr Thr 100 105 110 Ser Arg Phe Phe Asp Met Pro Leu Ser Glu Lys Gin Arg Val Leu Arg 115 120 125 Lys Ser Gly Glu Ser Val Gly Tyr Ala Ser Ser Phe Thr Gly Arg Phe 130 135 140 Ser Thr Lys Leu Pro Trp Lys Glu Thr Leu Ser Phe Arg Phe Cys Asp 145 150 155 160 Asp Met Ser Arg Ser Lys Ser Val Gin Asp Tyr Phe Cys Asp Ala Leu 165 170 175 Gly His Gly Phe Gin Pro Phe Gly Lys Val Tyr Gin Glu Tyr Cys Glu 180 185 190 Ala Met Ser Ser Leu Ser Leu Lys He Met Glu Leu Leu Gly Leu Ser 195 200 205 Leu Gly Val Lys Arg Asp Tyr Phe Arg Glu Phe Phe Glu Glu Asn Asp 210 215 220 Ser He Met Arg Leu Asn Tyr Tyr Pro Pro Cys He Lys Pro Asp Leu 225 230 235 240 Thr Leu Gly Thr Gly Pro His Cys Asp Pro Thr Ser Leu Thr He Leu 245 250 255 His Gin Asp His Val Asn Gly Leu Gin Val Phe Val Glu Asn Gin Trp 260 265 270 Arg Ser He Arg Pro Asn Pro Lys Ala Phe Val Val Asn He Gly Asp 275 280 285 Thr Phe Met Ala Leu Ser Asn Asp Arg Tyr Lys Ser Cys Leu His Arg 290 295 300 Ala Val Val Asn Ser Lys Ser Glu Arg Lys Ser Leu Ala Phe Phe Leu 305 310 315 320 Cys Pro Lys Lys Asp Arg Val Val Thr Pro Pro Arg Glu Leu Leu Asp 325 330 335 Ser He Thr Ser Arg Arg Tyr Pro Asp Phe Thr Trp Ser Met Phe Leu 340 345 350 Glu Phe Thr Gin Lys His Tyr Arg Ala Asp Met Asn Thr Leu Gin Ala 355 360 365 Phe Ser Asp Trp Leu Thr Lys Pro He 370 375 (2) INFORMATION FOR SEQ ID NO: 5: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 1490 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: cDNA to mRNA (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: Arabidopsis thaliana (vii) IMMEDIATE SOURCE: (B) CLONE: pAT2353 (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 5: GGTATCGATA AGCTTGATAT CGAATTCGAG GATCCGGGAC CATGGACAAA AACCCCAAAA 60 CTCTCAAGAA AAAAAAAAGA AAAGAAATGG CGATACTATG CACAACAACA TCTCCGGCAG 120 AGAAAGAACA CGAACCAAAA CAAGATCTTG AAAAAGACCA AACTTCTCCA CTAATCTTTA 180 ACCCTTCTCT TCTTAACCTC CAATCCCAAA TCCCAAACCA ATTCATTTGG CCAGACGAAG 240 AGAAACCTTC CATTGACATT CCAGAGCTCA ACGTCCCGTT CATCGATCTC TCAAGCCAAG 300 ACTCGACTCT TGAAGCTCCT AGAGTCATCG CAGAAGCTTG CACCAAACAC GGCTTCTTCC 360 TCGTCGTCAA TCATGGCGTC AGCGAGTCAC TAATAGCGGA TGCTCACCGT TTGATGGAAA 420 GTTTCTTCGA CATGCCTCTC GCCGGCAAAC AGAAAGCTCA GAGAAAACCC GGTGAGAGTT 480 GTGGCTATGC AAGTAGCTTC ACCGGCAGAT TCTCCACTAA GCTGCCATGG AAGGAGACTC 540 TCTCTTTTCA GTTTTCCAAC GATAATAGTG GCTCGAGAAC CGTTCAAGAT TACTTTTCCG 600 ATACATTAGG ACAAGAGTTC GAGCAGTTTG GGAAGGTGTA TCAAGACTAT TGTGAAGCAA 660 TGAGTTCTCT ATCACTCAAG ATCATGGAGC TTCTGGGCTT AAGTTTAGGC GTAAACCGAG 720 ACTATTTCCG AGGATTTTTC GAAGAGAACG ATTCGATAAT GAGGCTCAAT CATTATCCTC 780 CATGCCAAAC ACCAGATCTC ACGTTAGGTA CAGGACCTCA TTGTGATCCA AGTTCTTTGA 840 CCATCCTTCA TCAAGACCAT GTCAATGGCC TTCAAGTCTT TGTCGACAAT CAATGGCAAT 900 CCATTCGTCC CAATCCCAAG GCTTTCGTTG TCAATATTGG TGACACTTTC ATGGCTCTAT 960 CGAACGGGAT ATTCAAGAGC TGTTTGCATA GAGCGGTTGT GAATAGAGAG AGCGCGAGAA 1020 AATCGATGGC GTTTTTCTTG TGTCCGAAGA AAGACAAAGT GGTGAAACCA CCAAGTGATA 1080 TTTTGGAGAA GATGAAAACA AGAAAATACC CTGACTTCAC TTGGTCTATG TTCCTTGAGT 1140 TCACTCAAAA ACATTACCGA GCAGATGTGA ATACTCTCGA TTCCTTTTCT AATTGGGTTA 1200 TTACCAACAA CAATCCCATC TAAGAAACAA AATTATTTAC TATCTCAATC TTTTGTTTTT 1260 CTTTGGTTAC TTTGTGTCCT TTGTTCTCAT GGTGAAATGC ATTAAATTGC ATTTCAAAGT 1320 TTTAAACGTT TGTATATTGA TTGTTCCAAG CTTTAGACCA ATCCCTACCG TATGAGCTCG 1380 TTCAATGAAT AATTTGAATG AAAAATTCAA AGAAATTTTT CTTAAAAAAA AAAAAAAAAA 1440 AAAAAAAAAA AAAAAAAAAA AAAAAAAAAA CCATGGTACC CGGATCCTCG 1490 (2) INFORMATION FOR SEQ ID NO: 6: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 378 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: Arabidopsis thaliana (vii) IMMEDIATE SOURCE: (B) CLONE: zu pAT2353 (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 6: Met Ala He Leu Cys Thr Thr Thr Ser Pro Ala Glu Lys Glu His Glu 1 5 10 15 Pro Lys Gin Asp Leu Glu Lys Asp Gin Thr Ser Pro Leu He Phe Asn 20 25 30 Pro Ser Leu Leu Asn Leu Gin Ser Gin He Pro Asn Gin Phe He Trp 35 40 45 Pro Asp Glu Glu Lys Pro Ser He Asp He Pro Glu Leu Asn Val Pro 50 55 60 Phe He Asp Leu Ser Ser Gin Asp Ser Thr Leu Glu Ala Pro Arg Val 65 70 75 80 He Ala Glu Ala Cys Thr Lys His Gly Phe Phe Leu Val Val Asn His 85 90 95 Gly Val Ser Glu Ser Leu He Ala Asp Ala His Arg Leu Met Glu Ser 100 105 110 Phe Phe Asp Met Pro Leu Ala Gly Lys Gin Lys Ala Gin Arg Lys Pro 115 120 125 Gly Glu Ser Cys Gly Tyr Ala Ser Ser Phe Thr Gly Arg Phe Ser Thr 130 135 140 Lys Leu Pro Trp Lys Glu Thr Leu Ser Phe Gin Phe Ser Asn Asp Asn 145 150 155 160 Ser Gly Ser Arg Thr Val Gin Asp Tyr Phe Ser Asp Thr Leu Gly Gin 165 170 175 Glu Phe Glu Gin Phe Gly Lys Val Tyr Gin Asp Tyr Cys Glu Ala Met 180 185 190 Ser Ser Leu Ser Leu Lys He Met Glu Leu Leu Gly Leu Ser Leu Gly 195 200 205 Val Asn Arg Asp Tyr Phe Arg Gly Phe Phe Glu Glu Asn Asp Ser He 210 215 220 Met Arg Leu Asn His Tyr Pro Pro Cys Gin Thr Pro Asp Leu Thr Leu 225 230 235 240 Gly Thr Gly Pro His Cys Asp Pro Ser Ser Leu Thr He Leu His Gin 245 250 255 Asp His Val Asn Gly Leu Gin Val Phe Val Asp Asn Gin Trp Gin Ser 260 265 270 He Arg Pro Asn Pro Lys Ala Phe Val Val Asn He Gly Asp Thr Phe 275 280 285 Met Ala Leu Ser Asn Gly He Phe Lys Ser Cys Leu His Arg Ala Val 290 295 300 Val Asn Arg Glu Ser Ala Arg Lys Ser Met Ala Phe Phe Leu Cys Pro 305 310 315 320 Lys Lys Asp Lys Val Val Lys Pro Pro Ser Asp He Leu Glu Lys Met 325 330 335 Lys Thr Arg Lys Tyr Pro Asp Phe Thr Trp Ser Met Phe Leu Glu Phe 340 345 350 Thr Gin Lys His Tyr Arg Ala Asp Val Asn Thr Leu Asp Ser Phe Ser 355 360 365 Asn Trp Val He Thr Asn Asn Asn Pro He 370 375 (2) INFORMATION FOR SEQ ID NO: 7: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 9 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (v) FRAGMENT TYPE: internal (vi) ORIGINAL SOURCE: (A) ORGANISM: Cucurbita maxima (F) TISSUE TYPE: Endosperm (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 7: Val Phe Gly Gly Ser Asp Glu Ser Lys 1 5 (2) INFORMATION FOR SEQ ID NO: 8: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 6 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (v) FRAGMENT TYPE: internal (vii) IMMEDIATE SOURCE: (B) CLONE: zu Primer 1 (Beispiel 38) (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 8: Asn Tyr Tyr Pro Thr Cys 1 5 (2) INFORMATION FOR SEQ ID NO: 9: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 7 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (iii) HYPOTHETICAL: NO (v) FRAGMENT TYPE: internal (vii) IMMEDIATE SOURCE: (B) CLONE: zu Primer 2 (Beispiel 38) (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 9: Phe Val He Asn He Gly Asp 1 5 (2) INFORMATION FOR SEQ ID NO: 10: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 25 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vii) IMMEDIATE SOURCE: (B) CLONE: Primer 1 (Beispiel 38) (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 10: GCAAGCTTAA YTAYTAYCCN ACNTG 25 (2) INFORMATION FOR SEQ ID NO: 11: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 26 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vii) IMMEDIATE SOURCE: (B) CLONE: Primer 2 (Beispiel 38) (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 11: AARCANTADT TRTADCCNCT TAAGCG 26 (2) INFORMATION FOR SEQ ID NO: 12: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 174 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vi) ORIGINAL SOURCE: (A) ORGANISM: Arabidopsis thaliana (vii) IMMEDIATE SOURCE: (B) CLONE: pAt2204 (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 12: AATTACTACC CTACGTGTAT AAAACCAGAT CTCACACTAG GAACAGGACC TCATTGTGAT 60 CCAACATCTC TTACCATCCT TCACCAAGAC CATGTTAATG GCCTTCAAGT CTTTGTGGAA 120 AATCAATGGC GCTCCATTCG TCCCAACCCC AAGGCCTTTG TAATTAACAT CGGA 174 (2) INFORMATION FOR SEQ ID NO: 13: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 58 amino acids (B) TYPE: amino acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: peptide (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (v) FRAGMENT TYPE: internal (vi) ORIGINAL SOURCE: (A) ORGANISM: Arabidopsis thaliana (vii) IMMEDIATE SOURCE: (B) CLONE: zu Clone pAt2204 (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 13: Asn Tyr Tyr Pro Thr Cys He Lys Pro Asp Leu Thr Leu Gly Thr Gly 1 5 10 15 Pro His Cys Asp Pro Thr Ser Leu Thr He Leu His Gin Asp His Val 20 25 30 Asn Gly Leu Gin Val Phe Val Glu Asn Gin Trp Arg Ser He Arg Pro 35 40 45 Asn Pro Lys Ala Phe Val He Asn He Gly 50 55 (2) INFORMATION FOR SEQ ID NO: 14: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 28 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vii) IMMEDIATE SOURCE: (B) CLONE: Oligo (Beispiel 39a) (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 14: GAGAATTCTA AGTTGATAAT GGTTATTG 28 (2) INFORMATION FOR SEQ ID NO: 15: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 26 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: D.NA (genomic) (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vii) IMMEDIATE SOURCE: (B) CLONE: Oligo 1 (Beispiel 39b) (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 15: GAGAATTCAA AATGGCCGTA AGTTTC 26 (2) INFORMATION FOR SEQ ID NO: 16: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 27 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vii) IMMEDIATE SOURCE: (B) CLONE: Oligo 2 (Beispiel 39b) (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 16: GAGAATTCAG AAATGGCGAT ACTATGC 27 (2) INFORMATION FOR SEQ ID NO: 17: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 27 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: linear (ii) MOLECULE TYPE: DNA (genomic) (iii) HYPOTHETICAL: NO (iii) ANTI-SENSE: NO (vii) IMMEDIATE SOURCE: (B) CLONE: Oligo 3 (Beispiel 39b) (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 17: GAGAATTCAA AAATGGCAAC GGAATGC 27

Claims: What is claimed is: 1. DNA sequence which encodes a polypeptide exhibiting GA 20-oxidase activity. 2. DNA sequence according to claim 1, in which the polypeptide exhibiting GA 20-oxidase activity is capable of acting essentially on one or more of the following substrates: GA12, GA53, GA15 (open or closed lactone), GA44 (open or closed lactone), GA24, GA19 and GA23 3. DNA sequence according to claim 1 or 2, which is in the form of a cDNA clone. 4. DNA sequence according to any of claims 1 to 3, which encodes a GA 20-oxidase obtainable from plants or fungi, preferably from monocotyledonous or dicotyledonous plants, more preferably from dicotyledonous plants and most preferably from plants of the family Cucurbitaceae and Cruciferae, respectively. 5. DNA sequence according to claim 4, which encodes a GA 20-oxidase obtainable from Cucurbita maxima or a protein having at least 35 %, preferably at least 50 %, and most preferably at least more than 50% homology therewith. 6. DNA sequence according to claim 4, which encodes a GA 20-oxidase obtainable from Arabidopsis thaliana or a protein having at least 35 %, preferably at least 50 %, and most preferably at least more than 50% homology therewith. 7. DNA sequence according to any of claims 1 to 6, comprising a sequence corresponding to the open reading frame of the sequence shown in SEQ ID NO 1, SEQ ID NO 3 and SEQ ID NO 5, or an equivalent sequence through the degeneracy of the genetic code, including derivatives capable of hybridizing with the sequence shown in SEQ ID NO 1, SEQ ID NO 3 AND SEQ ID NO 5, and still encoding a polypeptide exhibiting GA 20-oxidase activity. 8. A substantially pure DNA as shown in SEQ ID NO 1 or a DNA having substantial sequence homology to the sequence shown in SEQ ID NO 1. 9. A substantially pure DNA as shown in SEQ ID NO 3 or a DNA having substantial sequence homology to the sequence shown in SEQ ID NO 3. 10. A substantially pure DNA as shown in SEQ ID NO 5 or a DNA having substantial sequence homology to the sequence shown in SEQ ID NO 5. 11. A method of preparing a DNA sequence which encodes a polypeptide exhibiting a GA 20-oxidase activity, comprising preparing a cDNA library from a suitable source organism, and screening this library by means of one of the conventionally applied screening systems. 12. A method according to claim 11, in which the screening is accomplished by means of an antibody against GA 20-oxidase or part of its amino acid sequence, or by testing for catalytic activity characteristic of the GA 20-oxidase. 13. A recombinant DNA comprising a DNA sequence according to any one of claims 1 to 10. 14. A recombinant polypeptide exhibiting GA 20-oxidase activity. 15. A recombinant polypeptide according to claim 14, which is capable of acting essentially on one or more of the following substrates: GA- , GA53, GA15 (open or closed lactone), GA44 (open or closed lactone), GA24, GA19 and GA23. 16. A recombinant GA 20-oxidase according to claim 14 or 15, which is obtainable from plants or fungi, preferably from monocotyledonous or dicotyledonous plants, more preferably from dicotyledonous plants and most preferably from plants of the family Cucurbitaceae and Cruciferae, respectively. 17. A recombinant GA 20-oxidase according to claim 16, which is obtainable from Cucurbita maxima or is a protein having at least 35 %, preferably at least 50 %, and most preferably at least more than 50 % homology with the native C. maxima GA 20- oxidase. 18. A recombinant GA 20-oxidase according to claim 16, which is obtainable from Arabidopsis thaliana or is a protein having at least 35 %, preferably at least 50 %, and most preferably at least more than 50 % homology with the native A thaliana GA 20- oxidase. 19. A recombinant GA 20-oxidase according to any of claims 14 to 18, having the amino acid sequence shown in SEQ ID NO 2, SEQ ID NO 4 and SEQ ID NO 6, or being a protein having at least 35 %, preferably at least 50 %, and most preferably at least more than 50 % homology with this amino acid sequence and having GA 20-oxidase activity. 20. A method of preparing a recombinant polypeptide exhibiting GA 20-oxidase activity, which comprises expressing in a suitable host organism a DNA sequence as claimed in any of claims 1 to 10 and 13. 21. A method according to claim 20, in which said expression takes place in a transformed host cell. 22. A transformed host cell comprising a recombinant DNA containing a DNA sequence encoding a polypeptide exhibiting GA 20-oxidase activity in operable linkage with expression signals including promoter and termination sequences which permit expression of said DNA in the host cell. 23. A chimaeric gene construct comprising a recombinant DNA containing a DNA sequence encoding a polypeptide exhibiting GA 20-oxidase activity in operable linkage with plant expression signals including promoter and termination sequences capable of causing the gene to express a polypeptide exhibiting GA 20-oxidase activity within a plant. 24. A chimaeric gene construct comprising at least a part of a reverse GA 20-oxidase nucleotide sequence, in operable linkage with plant expression signals including promoter and termination sequences capable of causing the reverse sequence to express antisense mRNA within a plant. 25. A chimaeric gene construct according to claim 23 or 24, wherein the promoter is an inducible promoter. 26. A chimaeric gene construct according to claim 23 or 24, wherein the promoter is a tissue-preferential or tissue-specific promoter. 27. A chimaeric gene construct according to claim 26, wherein the tissue-preferential or tissue-specific promoteris a pith-specific promoter. 28. A chimaeric gene construct according to claim 23 or 24, comprising in addition to the promoter and termination sequences further regulatory sequences of the 5' and 3' untranslated region. 29. A chimaeric gene construct according to claim 28, wherein the additional regulatory sequence is a sequence capable of regulating the transcription of an associated DNA sequence in plant tissues in the sense of induction or repression. 30. A chimaeric gene construct according to claim 29, wherein the regulatory sequence is inducible by a chemical. 31. A chimaeric gene construct according to claim 30, wherein the regulatory sequence is obtainable from a PR (pathogenesis- related) protein gene. 32. Vector comprising a chimeric gene construct according to any of claims 23 to 31. 33. A host cell transformed with a chimeric gene construct according to any of claims 23 to 31. 34. A host cell acording to claim 33, which is of bacterial or plant origin. 35. A transgenic plant cell or plant including its seed comprising stably integrated into its genome a DNA sequence according to any of claims 1 to 10. 36. A transgenic plant including its seed comprising a recombinant DNA containing a DNA sequence encoding a polypeptide exhibiting GA 20-oxidase activity in operable linkage with plant expression signals including promoter and termination sequences which permit expression of said DNA in the plant. 37. A transgenic plant including its seed comprising a reverse GA 20-oxidase nucleotide sequence or a part thereof in operable linkage with plant expression signals including promoter and termination sequences which permit transcription of said sequence or partial sequence to form antisense mRNA. 38. A transgenic cell or plant including its seed which is transformed with a chimeric gene construct according to any one of claims 23 to 31. 39. A transgenic plant according to any of claims 35 to 38 selected from the group consisting of tobacco, carrot, sunflower, tomato, cotton, Zea mays, Dactylis glomerata and wheat. 40. A transgenic plant according to any of claims 35 to 38, which is a monocotyledonous plant, preferably a graminaceous monocot. 41. A transgenic plant according to claim 40, which is a graminaceous monocot selected from the group consisting of Lolium, Zea, Triticum, Triticale, Sorghum, Saccharum, Bromus, Oryzae, Avena, Hordeum, Secale and Setaria. 42. A transgenic plant according to claim 41, which is a maize plant. 43. A transgenic plant according to claim 41, which is a wheat plant. 44. A transgenic plant according to claim 42, which is a Zea mays Elite inbred line Funk 2717. 45. Progeny or propagules, including seed, of a transgenic plant according to any one of claims or 35 to 44. 46. A method of identifying DNA sequences comprising a DNA region encoding a poly¬ peptide exhibiting GA 20-oxidase activity which method comprises preparing a cDNA or a genomic library from a suitable source organism and screening this library by means of hybridisation using a recombinant DNA according to any of claims 7 to 10 as a hybridisation probe. 47. A DNA sequence comprising a DNA region encoding a polypeptide exhibiting GA 20-oxidase activity obtainable by a method according to claim 46.

Inventors: GRAEBE JAN E, HEDDEN PETER, LANGE THEODOR, PHILLIPS ANDREW, GRAEBE, JAN, E., HEDDEN, PETER, LANGE, THEODOR, PHILLIPS, ANDREW
Applicants: GRAEBE JAN E, HEDDEN PETER, LANGE THEODOR, LONG ASHTON RESEARCH STATION, PHILLIPS ANDREW, GRAEBE, JAN, E., HEDDEN, PETER, LANGE, THEODOR, PHILLIPS, ANDREW
Application year: 1994
Main classification: C12N15
IPC codes: A01H5, C12N1, C12N5, C12N9, C12N15, C12Q1